Time-lapse Videotape Recordings Research Articles

Courtship in Desmognathine Salamanders: The Southern Dusky Salamander, Desmognathus auriculatus

-The courtship of the southern dusky salamander, Desmognathus auriculatus (Plethodontidae), is described for the first time. Most of a male's effort is expended in orienting to and stimulating (or 'persuading') his partner. Much of the stimulation provided by the male is tactile (nudging and rubbing), although he also exhibits behavior patterns associated with the transfer of courtship pheromones (snapping and pulling). Movements of the male's forelimbs may stimulate the female visually. The consummatory act of courtship is indirect sperm transfer by means of a spermatophore, and this stage of courtship appears identical in all desmognathines yet described. Courtship behavior patterns in the subfamily Desmognathinae are an apparent mosaic of ancestral and derived characters, with some evidence for homoplasy. Formal analyses of behavioral evolution await a robust phylogenetic hypothesis and detailed ethograms for multiple populations of all recognized taxa. The absence of lungs is a character shared by all salamanders in the family Plethodontidae (Duellman and Trueb, 1986). Reliance on cutaneous gas exchange may be a major constraint on the geographic distribution of these animals. The majority of taxa are found in relatively cool and moist habitats, especially in the montane regions of the Pacific Northwest and Appalachian Mountains of North America, and the cloud forests of Central America. An exceptional, but not unique, taxon is the southern dusky salamander, Desmognathus auriculatus (subfamily Desmognathinae), populations of which occur throughout the Gulf and Atlantic Coastal Plains of the southeastern United States. Winters typically are mild and summers warm and humid in these physiographic provinces. Well away from the mountains, D. auriculatus can be found in the organic debris along the shady margins of small streams, hypoxic pools and swamps. Little has been published on the natural history of the southern dusky salamander (but see Robertson and Tyson, 1950, for some observations of this species in eastern North Carolina). Here I report the first laboratory observations of this species' courtship and mating behavior. I then compare these to descriptions for other desmognathine salamanders, in anticipation of a formal, phylogenetic analysis of the evolution of courtship in this subfamily. MATERIALS AND METHODS Sexually mature D. auriculatus were collected in the summer of 1994 from several sites near the Savannah River Site in Aiken and Barnwell Counties, South Carolina (see Gibbons and Semlitsch, 1991). Most were found by raking through the organic debris on the margins of small pools. Desmognathus auriculatus is the only desmognathine that has been recorded in this part of South Carolina, although the presence of D. fuscus is possible (see Gibbons and Semlitsch, 1991). Each of my specimens was identified as D. auriculatus on the basis of body size, the presence of pale lateral spots, and the speckled appearance of the belly. Animals were transported to the laboratory in cooled containers, where they were maintained at approximately 15 C on a natural (Pullman, Washington) photoperiod. Salamanders were housed individually in plastic boxes measuring 9 x 17 x 31 cm, with a damp paper towel as substratum and a crumpled damp paper towel as a refuge. An ad libitum diet of vitamin-mineral dusted waxworms (moth larvae) was provided. I staged a total of seven heterosexual encounters between pairs of single males and females drawn from a pool of four males and two females. No two individuals were paired together more than once. Encounters were staged in a plexiglass observation arena measuring 17 x 17 x 5 cm, floored with a damp paper towel; no refuge was made available. Animals were introduced at approximately 1500 h and left together until 0800 h the following morning. All behavioral interactions were recorded under dim red illumination on a time-lapse videotape recorder (Panasonic AG-6010) using a low-light video camera (Panasonic WV-BD400).

In vitro measurement of orthodontic tooth movement in rats given beta-aminopropionitrile or hydrocortisone using a time-lapse videotape recorder.

In vitro tooth movement of rat molars in response to an orthodontic force was recorded using a time-lapse videotape recorder and analysed by a computer system. Rats received daily s.c. injections of beta-aminopropionitrile (BAPN, 300 mg/kg/day) or hydrocortisone (10 mg/kg/day) for a period of 7 days. After drug administration, the animals were killed and the mandibles dissected. The jaw was then held under a stereomicroscope with a haemostatic clamp and an elastic band was inserted between the first and second molars. The movements of reference points on the occlusal surfaces of the first and second molars were recorded for 20 hours using a time-lapse videotape recorder. Mesiolingual movement of the first molar and distobuccal movement of the second molar were observed. During the experimental period, the greatest amount of total tooth movement in the first and second molars was seen in the group pretreated with BAPN, less movement was observed in the control group, and the group pretreated with hydrocortisone exhibited the least amount of movement. The highest rates of tooth movement were observed during the initial hour in each of the groups, and decreased thereafter. The initial rates of movement were also greatest in the BAPN group, less in the control group, and least in the hydrocortisone group. These results indicate that treatment with BAPN accelerated experimental tooth movements in vitro and hydrocortisone treatment inhibited the movements, suggesting that, although a part of the tooth movement measured in this experiment was due to deformation of the alveolar bone, the mechanical properties of the periodontal ligament play an important role in the regulation of orthodontic tooth movement.

Integrity of myosin light chain kinase is essential for Ito cell contraction.

Hepatic sinusoidal Ito cells (fat storing cells) are believed to play a regulatory role on hepatic sinusoidal blood flow through their contraction. The detailed mechanism of contraction of Ito cells, however, is still unknown. The present study was undertaken to clarify the effect of new myosin light chain kinase inhibitor, wortmannin, on Ito cell contraction. Ito cells prepared from rat liver were cultured for 4 days before the study. The contraction of Ito cells, which was monitored and analysed by time-lapse video tape recording, was triggered by addition of endothelin-1. Wortmannin pretreatment for 1 h inhibited endothelin-induced Ito cell contraction dose-dependently. Therefore, the integrity of the actomyosin system is essential for Ito cell contraction and normal sinusoidal blood flow.

The behavior of chick gastrula mesodermal cells under the unidirectional tractive force parallel to the substrata.

Advancement of leading lamellae of a migratory cell inevitably causes a strain inside the cell body. We investigated the effect of the tension arisen inside a mesodermal cell on its behavior by pulling the cell body unidirectionally along the substratum. Chick gastrula mesodermal cells, known as highly migratory, were dissociated into single cells in sodium citrate buffer, conjugated with paramagnetic beads activated by tosyl-residue (4.5 microns in diameter) and seeded onto coverglasses coated with fibronectin. After the cells spread on the substratum and protruded cellular processes in all directions, they were exposed to a non-uniform magnetic field by a magnet. Thus the cells bearing the beads were pulled with a force in the order of 10(-10) N. The behavior of such cells was recorded with a time-lapse video taperecorder and assessed quantitatively. Shortly after the magnetic force was applied, the beads stuck to the cells were aligned in tandem along the line of magnetic force at the site for the magnet. Subsequently, they frequently came to extend their leading lamella precisely counter to the traction on the line of the beads. Observation with scanning electron microscope revealed that a large part of the beads attached to the cells were wrapped in the cell membrane. In this condition, the cells were stretched locally between the attachment site of the beads and adhesion plaques beneath the leading edge, which was formed in a direction away from the traction. It was proved statistically that such cells tended to locomote away from the magnet at the 0.1% significance level with Hotelling's T2-test. In contrast, the mesodermal cells free of the artificial traction in three kinds of control experiments did not show such a preference in the direction of locomotion. These results proved that migratory cells tended to move in the direction away from the tractive force parallel to the substratum, suggesting that advancement of a leading lamella is accelerated when it is stretched along the direction of projection by a mechanical force of sufficient strength. Implication of this finding to the mechanism of cell locomotion will be discussed.

Analysis of sexual behavior in rams (Ovis aries).

In this study, a matured ram was paired with an estrus ewe and sexual behavior was investigated. All the behavior was recorded by a time-lapse video tape recorder from the start of pairing. The series of unit movements comprising the sexual behavior, the mounting series (MS), was extracted from the record and analyzed quantitatively (n = 774). The MS starts from ram's approaching or following a ewe and ends by ram's mounting on a ewe. The sexual behavior was consisted of the following eight unit movements, following or approaching (F/A), chin resting (CR), flehmen (Fl), mounting (Mo), nosing (No), nudging (Nu), pushing (Pu) and twisting (Tw). Analysis of a frequency of any combinations of two unit movements consisted of preceding and succeeding ones, observed in the MS was conducted by cell-by-cell test using the transitional matrix to make a flow-diagram of the ram's sexual behavior. As a result, the pattern of unit movements, F/A-Tw-Nu-CR-Mo, formed a main route of the MS, whereas the repertoire of a sequential pattern increased by diverging. Though Fl and No didn't lead to mounting directly, these movements associated with olfactory perception also belonged to sexual behavior and may have independent function from other six unit movements that constitute the MS.

Migration and contraction of cultured Ito cells

The migration and contraction of cultured Ito cells were recorded continuously using a time-lapse videotape recorder. Upon the initiation of cell division, all the protrusions from the Ito cell quickly retracted back into the Ito cell, and the cell assumed the shape of a small sphere. The rounded cell migrated quickly on the surface of the culture flask to a new location and then flattened rapidly, forming many protrusions in all directions following cell division. Thirty minutes after the addition to the culture medium of the vasoconstrictors, such as endothelin-1, substance P or Ca-ionophore, the Ito cells gradually began to retract these protrusions and the cell bodies assumed a spindle shape. The cells continued to gradually contract over a 4 h period. These results suggest the possibility that Ito cells are able to migrate to a distant location within the liver, following mitosis. In the present study, clear evidence of contraction of the Ito cells following incubation with vasoactive substances suggests that the Ito cells may play an important role in controlling blood flow by narrowing the lumen of the sinusoids. Furthermore, since Ca-ionophore caused contraction, the results indicate the possibility that contraction of Ito cells by treatment with vasoactive stimulators may be mediated by changes in the concentration of calcium ions within the cytoplasm of the cells.

Calcium Waves Accompany Contraction Waves in the Oryzias latipes (Medaka) Blastoderm.

We examined 15 embryos and saw regular, periodic pulses of light in 9 of them. These pulses arose in the pacemaker region, spread across the blastoderm, and ended on the opposite side of the blastoderm, near the embryonic axis. We saw no pulses in two eggs that had not quite developed to the stage at which they begin to contract rhythmically. The interval between calcium pulses at the pacemaker (155 f 11 s, x + SEM, n = 9 embryos) was estimated by counting photons for 9-32 min in a 15-pixel-square box drawn over this region (Fig. 1); the interval between mechanical pulses at the pacemaker (146 t 7 s, X f SEM, n = 6 embryos) was estimated from an analysis of timelapse video tape recordings. The velocity of the calcium wave (11.9 f 1.1 p/s, X + SEM, n = 7 embryos) was estimated by comparing the timing of the pulses at the pacemaker with those near the embryonic axis. This velocity is in the range of the fast calcium waves that are propagated by calcium-induced calcium release or by some related reaction-diffusion process (5). The calcium pulses and waves described herein are similar to the contraction waves in the following ways: 1) they both originate in the pacemaker region of the blastoderm, propagate across the blastodisc, and extinguish near the embryonic axis; 2) they have similar periods; and 3) they propagate at similar velocities.

Metamorphosis of behavior in the bullfrog (Rana catesbeiana).

This study describes the development of different spontaneous and elicited behaviors of frogs and their relationship to morphological, physiological, and ecological changes of metamorphosis. Tadpoles were studied at all stages of development from Stage XVIII, the onset of metamorphosis, to Stage XXV, when metamorphosis of the froglets is complete. Behaviors examined included development of forelimb postural support, postural responses to vestibular stimulation, the hindlimb withdrawal reflex, the corneal reflex, ocular mobility, and habitat preference. Results showed that these behaviors differ markedly in their timing and rate of maturation. Forelimb postural support and postural responses to vestibular stimulation improved gradually between Stages XX and XXV. In contrast, the threshold of the hindlimb withdrawal reflex remained essentially unchanged until Stage XXV, when it increased suddenly and dramatically. The corneal reflex appeared suddenly at Stage XXI with a threshold similar to that of juvenile frogs. The ability to move the eyes in response to visual or vestibular stimulation was pronounced in tadpoles, but gradually declined between Stage XVIII and Stage XXV, so that froglets showed almost no ocular mobility. The preference of metamorphosing frogs for deep water, shallow water, shoreline, or land were examined in an aquarium during a 24-hr observation period using time-lapse videotape recordings. Results showed that tadpoles spent progressively less time in deep water and shallow water as metamorphosis proceeded. Preference for land emerged suddenly at Stage XXII and remained high thereafter. There were no stage-related differences in preferences for the shoreline.

The morphogenetic sequence followed by migrating slugs of Dictyostelium discoideum during reentry into the fruiting mode

Given the appropriate environmental cues, a migrating slug of Dictyostelium discoideum can, at any time, stop migrating, reenter the fruiting mode, and complete fruiting body construction over approximately an 8 h period. The reentry sequence exhibited by single slugs of known size and developmental condition has been documented in still photomicrographs and time-lapse videotape recordings. Reentry, culminating in the construction of a single fruiting body, has been found to involve a complex series of concerted morphogenetic movements by the slug tip and posterior regions which are remarkably invariant both in pattern and timing. At a frequency positively correlated with slug length, a variant scenario is impressed upon this basic sequence that leads to the formation of multiple fruits. The latter involves one or more transverse splits within the posterior region that can be preceded, attended, or succeeded by the appearance of additional apical tips in (relatively) anterior, medial, or posterior locations. The paradigmal sequences described here can serve as topographic groundwork upon which to construct or with which to test formal models of morphogenetic regulation. Repeated examinations of the videotapes have given us the impression that slug reentry resembles a reprise of aggregation involving the movement of the posterior region as a single outlying stream toward and under the tip, accompanied over the 2–2.5 h period by the accelerated progression of the tip and underlying region to the Mexican Hat stage. An earlier study [3,7] had shown that slug reentry triggers the quantal resynthesis of aggregation-associated proteins such as UDPG-pyrophosphorylase and UDP galactosyl transferase plus a delayed first round of UDP Gal-4-epimerase, a post-aggregation protein uniquely associated with the fruiting mode. It is noteworthy that the same pattern of protein synthesis is exhibited by cells mechanically dispersed from aggregates after 16–18 h development while they (rapidly) reaggregate and recapitulate previously accomplished morphogenesis [10].

Quantification of the locomotive behavior of polymorphonuclear leukocytes in clot preparations

Time-lapse videotape recordings of polymorphonuclear leukocytes (PMNs) from clot preparations were used to quantify the locomotive behavior of individual PMNs from normal subjects. Tracings derived from the videotapes allow one to quantify multiple parameters of the locomotive behavior of PMNs--direction, distance, rate, and angle of turn. The results obtained are reproducible from subject-to-subject and from preparation-to-preparation. The method allows the investigator to record the locomotive behavior of 100 cells simultaneously within a 5- min period and analyze the recording as time permits. We utilized this technique to compare the locomotive behavior of slow and fast PMNs (arbitrarily defined as cells that move less than or equal to 7.0 micrometer/min and greater than 7.0 micrometer/min mean rate of locomotion, respectively). The studies show that slow and fast PMNs, thus defined, differ not only in mean rate of locomotion but also in their rate of locomotion during periods of active locomotion, in the number of periods of inactivity/PMN/5 min (slow = 1.65 +/- 0.31; fast = 0.36 +/- 0.12), and in their turning behavior as measured by angle of turn (slow = 92 degrees +/- 39 degrees; fast = 39 degrees +/- 35 degrees). These results show that human PMNs from clot preparations are remarkably heterogeneous in their locomotive behavior, and the results suggest this heterogeneity is due to endogenous differences within cells.

Quantification of the Locomotive Behavior of Polymorphonuclear Leukocytes in Clot Preparations

Time-lapse videotape recordings of polymorphonuclear leukocytes (PMNs) from clot preparations were used to quantify the locomotive behavior of individual PMNs from normal subjects. Tracings derived from the videotapes allow one to quantify multiple parameters of the locomotive behavior of PMNs--direction, distance, rate, and angle of turn. The results obtained are reproducible from subject-to-subject and from preparation-to-preparation. The method allows the investigator to record the locomotive behavior of 100 cells simultaneously within a 5-min period and analyze the recording as time permits. We utilized this technique to compare the locomotive behavior of slow and fast PMNs (arbitrarily defined as cells that move less than or equal to 7.0 micrometer/min and greater than 7.0 micrometer/min mean rate of locomotion, respectively). The studies show that slow and fast PMNs, thus defined, differ not only in mean rate of locomotion but also in their rate of locomotion during periods of active locomotion, in the number of periods of inactivity/PMN/5 min (slow = 1.65 +/- 0.31; fast = 0.36 +/- 0.12), and in their turning behavior as measured by angle of turn (slow = 92 degrees +/- 39 degrees; fast = 39 degrees +/- 35 degrees). These results show that human PMNs from clot preparations are remarkably heterogeneous in their locomotive behavior, and the results suggest this heterogeneity is due to endogenous differences within cells.

Brain state and body position. A time-lapse video study of sleep.

Human sleep is characterized by episodes of immobility and by major body movements occurring in phase with the EEG sleep cycle. Using time-lapse videotape recording and electrophysiological monitoring, we studied the sleep of four normal subjects to determine the relationship of the movements to sleep cycle phase and the consistency of the power of the movement data to quantify sleep parameters. We were able to measure sleep latency and to predict the time of occurrence of non-rapid eye movement sleep episodes in our subjects from the video movement data alone. In addition, we discovered evidence of small body movement specific to rapid eye movement sleep.

Correlation of the Biologic Effects and Binding of Cytochalasins to Human Polymorphonuclear Leukocytes

Treatment of human PMNs with cytochalasins (CE, CD, CB, and H2CB) results in alteration of cell morphology and inhibition of cell motility. Morphological changes are similar to those reported for nonamoeboid fibroblasts--rounding, zeiosis, and arborization. Mean cell velocity of PMNs, as measured by quantitative analysis of time-lapse videotape recordings, was reduced to 0.1 micron/min (control, 7.3 +/- 4.2 micron/min). Phagocytosis by PMNs, as measured by phagocytosis of latex beads, was inhibited by 75%. The relative potency of the cytochalasins for inducing morphological change or for inhibiting locomotion and phagocytosis is similar to their relative potencies for affecting non-amoeboid cells: CE greater than CD greater than CB greater than or equal to H2CB. Quantitative binding of 3H-CB to purified PMNs under equilibrium conditions reveal two types of specific CB binding sites: high-affinity sites (KD approximately 3 x 10(-7) M, 3 x 10(6) sites/cell) and low affinity sites (KD approximately 2 x 10(-6) M). The relative affinities of the cytochalasins for the high-affinity and low-affinity CB binding sites parallel their relative potencies for inducing biologic effects (i.e. CE greater than CD greater than CB greater than or equal to H2CB).

Correlation of the biologic effects and binding of cytochalasins to human polymorphonuclear leukocytes

Treatment of human PMNs with cytochalasins (CE, CD, CB, and H2CB) results in alteration of cell morphology and inhibition of cell motility. Morphological changes are similar to those reported for nonamoeboid fibroblasts--rounding, zeiosis, and arborization. Mean cell velocity of PMNs, as measured by quantitative analysis of time-lapse videotape recordings, was reduced to 0.1 micron/min (control, 7.3 +/- 4.2 micron/min). Phagocytosis by PMNs, as measured by phagocytosis of latex beads, was inhibited by 75%. The relative potency of the cytochalasins for inducing morphological change or for inhibiting locomotion and phagocytosis is similar to their relative potencies for affecting non-amoeboid cells: CE greater than CD greater than CB greater than or equal to H2CB. Quantitative binding of 3H-CB to purified PMNs under equilibrium conditions reveal two types of specific CB binding sites: high-affinity sites (KD approximately 3 x 10(-7) M, 3 x 10(6) sites/cell) and low affinity sites (KD approximately 2 x 10(-6) M). The relative affinities of the cytochalasins for the high-affinity and low-affinity CB binding sites parallel their relative potencies for inducing biologic effects (i.e. CE greater than CD greater than CB greater than or equal to H2CB).

Video intensification microscopy (VIM) as an aid in routine fluorescence microscopy.

Video intensification microscopy (VIM), in which a highly sensitive television camera is combined with fluorescence microscopy and a timelapse video tape recorder (Willingham and Pastan 1978), is becoming widely used for studying movements of fluorescent probes on living cells. In our experience, the VIM system is also extremely convenient for more conventional fluorescence microscopy of fixed tissues. The advantages of VIM are greatest in applications where convenience in handling and recording images from a large number of specimens is more important than achieving the best possible optical image quality.

Failure of Mammalian Prolactin to Induce Incubation Behavior in Chickens and Turkeys

Three experiments on a high-broody strain of chickens that had not been selected for egg production for 50 generations and one experiment on a commercial strain of turkeys were conducted to test the effectiveness of mammalian prolactin (NIH-S10) in inducing regression of the ovary and incubation behavior. In two experiments on chickens, environmental factors known to favor the expression of broodiness were provided, and four components of nesting or incubation behavior were monitored continuously during the light period with a closed-circuit television system and timelapse videotape recorder. Although all doses of prolactin used caused regression of large ovarian follicles, none induced incubation behavior in either chickens or turkeys. Some prolactin-injected chickens occasionally displayed the covering stance of maternal behavior.An explanation for the discrepancy between these results and the results of studies conducted more than 20 years ago, in which mammalian prolactin was highly effective in inducing incubation behavior in chickens, may lie in differences in purity of the prolactin preparations used.

Social Influences On Biological Rhythms

Little attention has been given to the influence that social factors may have on biological rhythms. We maintain that this neglect stems from historical and technological circumstances in that most research in chronobiology has been aimed to discover the physiological basis for rhythmicity and that it is very difficult to study the rhythms of interacting animals. We review selected elements of the somewhat scattered literature that deals with social influences on circadian, ultradian and infradian rhythms. We find that social factors have been shown to result in the synchronization, desynchronization and disruption of biological rhythms in a wide range of organisms. By employing a time-lapse video tape recording system we were able to study the individual activity of interacting tegu lizards (Tupiranmbis teguixin). We found that some individuals demonstrated (1) social synchronization, (2) the formation of time-territories, (3) free-running rhythms against a LD 12:12 lighting schedule, and (4) apparent arrhythmicity. We related these phenomena to the social hierarchy of the lizards. Lizards ranked intermediate often occupied time-territories separate from the dominant lizard, and under certain conditions the lowest ranking lizard exhibited a free-running rhythm that was completely uncoupled from the lighting cycle. Under other conditions the lowest ranking lizard was socially synchronized. Also using closed circuit television techniques, we studied the running wheel rhythms of three individually marked female laboratory rats housed in the same cage in continuous dim red light. The rats could compete for the running wheel by synchronizing their activity or minimize competition by desynchronizing their activity. An inspection of the raw activity data revealed that omega X was displaced from D and S, thus occupying a separate time-territory, while D and S were closely ranked socially and closely synchronized in time. Cosine curves were fit by computer to the data of each rat using the least squares method. The percent rhythm (the percent of the total variability explained by the cosine curve) and the period length (the duration of one complete cycle of the rhythmic variation) proved to be particularly useful. We found that the free-running period lengths of D and S were nearly identical while that of omega X was quite different. So omega X's rhythm was not only displaced but also uncoupled from D and S. While housed with D and S, omega X's percent rhythm was very low and erratic. However, when D and S were temporarily removed from the activity cage, the percent rhythm of omega X rose markedly and its period length increased to a value nearly identical to that of D and S from before. Upon reintroduction of D and S to the home cage, omega X became displaced from the latter : its percent rhythm dropped dramatically and its free-running period length was again much different from D and S. We explore the possibilities (1) that disturbances of the timing of rhythms could affect individual fitness at the level of ecological and social intergration, (2) that crowding may cause rhythm reschedulings and disruptions that produce effects similar to those documented in jet-lag, (3) that time-territoriality could be a mechanism involved in the partitioning of resources among individuals in natural populations. Finally, (4) commonly housed animals even in controlled laboratory environments can modify one another's activity and perhaps physiological rhythms. This could confound attempts to control for biological rhythmicity using controlled lighting schedules. Thus, an awareness of the interaction of social behavior with rhythms may help physiologists and behaviorists to collect more reproducible data in the future.

Analytical studies on migrating movement of the pseudo-plasmodium ofDictyostelium discoideum

Migrating movement of a pseudoplasmodium (slug) of the cellular slime mouldDictyostelium discoideum was analyzed using a time-lapse video tape recorder. Since slugs usually migrated with repeated interruptions of advance, migrating velocities were measured only within a period of forward movement. On the basis of some known facts and assumptions, a dynamical model for slug movement was formulated, which consists of motive force generated by slug cells against their intrinsic resistance and resistance of slime sheath at the tip. The migrating velocity of a slug depended neither on its width nor its volume, but solely on its length. Under any experimental conditions tested, a linear relationship always held between reciprocals of the two variables. The results were in good agreement with predictions of the model. Quantitative analyses of experimental results by the use of the model lead to the conclusions that a decrease in velocity at a low temperature is due to an increase in resistance of slime sheath at the tip, but that a decrease in velocity during prolonged migration is due to a decrease in motive force of constituent cells. An anterior isolate dissected from a slug migrated at a velocity greater than that of an intact slug of the same length. This was interpreted by the model to be due to the fact that the anterior cells have greater motive forces and intrinsic resistances than the posterior cells. The heterogeneous distributions of the two variables in the cell mass is discussed in reference to the mechanism of sorting out of cells.

Night-Waking in Infants During the First Year of Life

Two groups of infants, 2 and 9 months of age, were monitored for one night by time-lapse videotape recording in the natural setting of their homes. Developmental changes in sleep-wake state proportions, ease of falling asleep, nighttime waking patterns, maternal interventions, and sleeping through the night were observed. A suggestion of differential parental handling of male infants was noted. Further research to clarify some of these issues is indicated.

Entry of Cancer productus to baited traps

Ease of finding the entrance was shown to be an important variable determining the effectiveness of baited crab traps. Traps for Cancer productus should be designed so the bait odour leads the crab to the trap entrance, not just to the trap. The operation of both top and side entry traps was observed in a large tank with the aid of closed circuit television and a time lapse videotape recorder. Crabs responding to the bait first encountered the side of a trap directly downstream of the bait. If the entrance was not at this point their search consisted of short excursions to the right and left and sometimes up the side of the trap. Only 27% of the approaches to the top entry trap resulted in crabs entering even though the entrance was but 30 cm from the point on the trap directly downstream of the bait. Only 7% of approaches to the side entry trap set with opposing entrances perpendicular to the current gained entry even though the entrances were but 40 cm from the point on the trap directly downstream of the bait. For the side entry trap set with entrances parallel to the current, giving one entrance directly downstream from the bait, 65% of the approaches resulted in entry. Most crabs that did not gain entry left the vicinity of traps as a result of being chased away by other crabs on the outside or after prolonged but unsuccessful searching for the entrance. Trap saturation was apparent in both trap types and was presumed due to the crabs inside traps intimidating those outside traps which would have otherwise entered.