Dorsal Field Research Articles

Spectral sensitivity of the red and yellow oil droplet fields of the pigeon (Columba livia).

THE function of the brightly coloured oil droplets situated within the cone receptors of the avian retina has long been the subject of debate1–4. Among other hypotheses it has been suggested that they reduce glare and chromatic abberation1, remove unwanted short-wavelength sensitivity2, and have a role in colour vision3–5. The transmission spectra of the droplets in the visible spectrum are typically those of short wavelength cut-off filters5,6–8, due to the presence in high concentration of carotenoids of dietry origin9–11. Recent evidence from microspectrophotometry suggests that the droplets filter the light reaching the visual pigment in the receptor's outer segment, resulting in the modification of the sensitivity functions of some of the individual receptors, from the broad band sensitivity of the visual pigment alone to a narrow band one12,13. It is also known that marked differences occur in the proportions of the variously coloured droplets between species, and also between different parts of the retina of a given species4,14–16. In the pigeon (Columba livia) the retina is divided into two distinct areas, known as the red and yellow fields, defined by their oil droplet populations. The red field is in the dorsal retina (frontal–ventral visual field), whereas the yellow field is in the ventral retina (dorsal visual field): the two fields differ in both the type and number of broad and narrow band receptors present, as well as in receptor density and the neural complexity of the retina13,17,18. We report here clear differences in the photopic spectral sensitivity of the two fields, determined behaviourally, and suggest that these reflect a difference in the colour vision mechanisms of the two areas.

An analysis of the spatial distribution of ciliary units in a ciliate, Euplotes minuta

Six to eleven longitudinal ciliary rows are arrayed over the dorsal surface of the ciliate Euplotes minuta. Forty-two to 129 ciliary units are distributed among these rows. The number of rows depends on genotype, clonal age, and vegetative ancestry, while the total number of units is controlled partly by the number of rows and also by the separate action of genetic and environmental factors. 2. The pattern of distribution of units among different rows of non-dividing cells can be analysed on the basis of the percentage of the total unit complement of the cell that is found in each individual row. If the assumption is made that ciliary rows are uniformly spaced over a dorsal field whose width is independent of the number of rows, then it can be shown that units are distributed among rows according to a relatively invariant spatial pattern. The form of this pattern remains the same in the face of variation in the absolute number of rows and of units. 3. Prior to cell division new units develop anterior and posterior to old units situated within the equatorial zone of each row. About one-half of the original units are included within this zone. The cell fission line develops within this zone such that the total number of units passed to the anterior and posterior division products are about equal. 4. The pattern according to which units of different zones (proliferating and non-proliferating) are distributed among different rows has been mapped in cells that have completed the process of proliferation of units but have not yet completed cell division. The results of this mapping show that the pattern of distribution of units in the equatorial zone at the conclusion of proliferation is not the same as the overall pattern in non-dividing cells. Further analysis indicates that the geometry of proliferation can be most simply represented as a result of two superimposed processes, one of which is the recruitment of old units into the zone of proliferation, while the other is the intensity of proliferation, i.e. the number of new units formed adjacent to each old unit. Both recruitment and intensity have constant values in the central region of the dorsal field, while recruitment is higher and intensity lower near both margins. The recruitment and intensity distributions are mutually nearly reciprocal, with slight asymmetries that formally account for the more dramatic asymmetry of the pattern of non-dividing cells. 5. A dualistic hypothesis is formulated for the control of the formation of new ciliary units within ciliary rows. The position of each new unit is largely controlled locally in relation to pre-existing units, while the decision of whether or not new units will develop at all, and how many will be formed, depends on superimposed positional systems operating within the context of the entire dorsal surface.

Cortico-striatal evoked potentials in the monkey ( Macaca mulatta)

A systematic study has been made of the topographic organization in the striatum of evoked potentials elicited by stimulation of the cerebral cortex in unanesthetized, comatose monkeys ( Macaca mulatta). Stimulation of the dorsal field of the prefrontal convexity elicited potentials primarily in rostral portions of the caudate, while stimulation of the ventral field of the prefrontal convexity elicited potentials in ventromedial areas of the putamen. Stimulation of different points on the precentral and postcentral gyri revealed a distinct somatopic organization of evoked responses in the putamen, although responsive zones in the putamen to precentral and postcentral stimulation slowed almost total overlap. An overlap of responsive zones to stimulation of the dorsal prefrontal convexity and the premotor area (area 6) was found in the dorsolateral part of the rostral caudate, while a zone of overlap of responses to stimulation of the ventral prefrontal convexity and “hand” motor area of the precentral gyrus was found in the ventromedial area of the putamen near the commissural level.

Descriptive Enibryogeny of the Mygalomorph Spider Antrodiaetus unicolor1,2

Material for the study of the embryogeny of the mygalomorph spider, Antrodiaetus unicolor (Hentz) (Araneae: Antrodiaetidae), was obtained from gravid females collected in North Carolina and transferred to test tubes, in which they oviposited. The eggs were incubated at 24—26°C in paraffin oil. Stages were fixed in alcoholic Bouin's and dehydrated for whole mount and sectioned preparations. Shortly after fertilization, the yolk became arranged into columns. Between these columns, cytoplasm extended from the centroplasm to periplasm. The fertilization (vitelline) membrane, surrounded by the chorion, overlaid the periplasm. As cleavage progressed, the yolk shifted into cones while the cleavage cavity became established. Once the cleavage nuclei reached the periplasm, the uppermost portion of the yolk spheres commenced to fall onto the lower yolk portion closing the cleavage cavity. This contraction phase was completed 6 days after oviposition. During gastrulation, the primitive cumulus arose from the primitive plug and migrated to the periphery of the egg. With subsequent dissolution of the cumulus, the dorsal field widened, and the beginning protozonites began to form around the abdominal pole. At least 5 segments were visible between the cephalic and caudal lobes. With the development of the cheliceral segment, the first 2 opisthosomal segments appeared. Subsequent opisthosomal development entailed the formation of succesive segments until the maximum number of 12, including the caudal lobe, was reached. The opisthosoma normally consisted of a preabdomen and postabdomen, the latter projecting anteriorly along the ventral portion of the embryo. Both the pre- and postabdomen contributed to the abdomen of the foetus. Reversion commenced following the formation of the last opisthosomal segment and was completed within 2½ days. Hatching occurred 20½ clays following oviposition.

Cortical morphogenesis in Paramecium aurelia following amputation of the anterior region

AbstractThe most anterior approximately 35 μ of the 49–50 μ long anterior region was removed from many paramecia by a transverse cut. The challenge imposed by the amputation met with the following responses in lines of successive proters (anterior products of fission). Restitution of the anterior region in successive proters. Most of the restitution occurred at the first fission which yielded proters having anterior region about 55% (as compared with the approximately 30% remaining after amputation) and posterior regions 68% of normal length. Return to normal was nearly complete after the eighth fission. Incomplete kineties in successive proters. The anterior termini of incomplete kineties came to be located more and more posteriorly in the course of successive fissions as growth occurred anterior to them. When the anterior termini came to be posterior to the fission plane, they were lost from the proters formed at this and subsequent fissions. Proters with reduced kineties were slenderer than normal. Dorsal kinety pattern in the proters. On the dorsal field, after all short kineties were lost from the proters, the remaining kineties were normally oriented anterior‐posteriorly. However, the normal arrangement of the anterior termini of kineties at the suture, on the dorsal anterior tip of the proters, was lacking. Ventral kinety pattern in the regenerated anterior region. Regenerated anterior regions possessed normal or nearly normal ventral kinety patterns. Deviations from normal were minor. The preoral suture. Normally this is a clear space at the juncture between the anterior ventral right and left field. The regenerated part of the suture was atypical: the clear space was lacking. Inheritance and variation of total number of kineties around the cell. In a slender clone, the mean number of kineties was 67 as compared with 75 in an uncut control clone. The difference was inherited for many fissions, but not permanently. Normally, the number of kineties decreases slowly when fission rate is low due to limitation of food and rises slowly when excess food is supplied. Abnormal buccal structures. Cuts made close to the vestibule, but not those further from the vestibule, resulted in death or in abnormal clones with defective buccal structures of various sorts.

The Mechanism and Efficiency of Sound Production in Mole Crickets

ABSTRACT Sound production in the mole crickets Gryllotalpa vineae and G. gryllotalpa is compared with that in Gryllus campestris. In all species action of the plectrum of the left forewing on the file or pars stridens of the right wing causes the harp areas of both wings to vibrate in phase with each other. As the lateral and dorsal fields of the wing are coupled flexibly, the dorsal field resonates freely. The available muscular power of G. vineae is about 3·5 mW., of G. gryllotalpa about 1 mW., and of Gryllus about 1·2 mW. The mesothoracic musculature of Gryllotalpa is fairly similar to that of Gryllus. The calling song of G. vineae has a fundamental frequency of 3·5 kHz, a pulse length of 8 msec, and a pulse interval of 14 msec, at 16°C. The song is very pure with a second harmonic of —26 dB. Simulations of the song made with modulated oscillators are of similar purity; the song can be regarded as a modulated pure note. The sound distribution has been measured, and from the area of an isobar plot and calculation of the mean power of each pulse, the total mean sound power output is 1·2 mW. and the peak power 3 mW. The efficiency of conversion of muscular to acoustic power is about 35%. G. vineae builds a double-mouthed horn-shaped burrow for singing. This contains a bulb which probably tunes the horn to act as a resistive load to the vibrating wings. The double mouths act as a line source with directional properties which concentrate the sound in a disk above the length of the burrow. The probable advantage of a directed sound output in attracting mates is considered; the disk-shaped pattern will be better than a hemispherical pattern of similar power. G. gryllotalpa also builds a hom, but this is larger than that of G. vineae and the song frequency is far lower, at 1·6 kHz. Although the sound power is far lower, about 2·5 × 10−5 W., the horn appears to act as a resistive load to the wings. Gryllus produces only about 6 × 10−5 W. at 30°C. This is attributed to the small size and hence low radiation resistance of the wings. Estimates are made of inertial losses that occur in sound production and these are shown to account for a substantial part of the mechanical power in the systems of both G. vineae and Gryllus.

Dorsal root sensory fields of the intestine

Dorsal root sensory fields of the intestine

Additional notes on the adult and larva ofsiboglinum fiordicumand on the possible mode of tube formation

Abstract S. fiordicum and S. holmei appear to be closely related. The distinction between the two is to be found in the “zone of thickened papillae” and the postannular region. As the hind end (anchor) is unknown for S. holmei the question as to whether these two species should be classified as a single species cannot at this juncture be contemplated. The bridle is considered as the tool by means of which the animal smears the exudate onto the inner surface of the tube. The larvae of S. fiordicum develop the bridle before they leave the maternal tube. The larval dorsal ciliary field divides into an anterior region which is lost in the adult, and a posterior region which is retained as the dorsal ciliary field of the metameric region.

ORGANIZATION OF THE VISUAL PROJECTION UPON THE OPTIC TECTUM OF SOME FRESHWATER FISH.

AbstractIn four species of freshwater fish, bass, carp, bluegill and goldfish, the topographical relations of the visual field with the contralateral optic tectum were investigated, using a small light as stimulus in the visual field and recording the electrical response of the tectum with a metal microelectrode. The results show a precisely organized visual projection onto the contralateral tectum in which the anterior visual field lies anteriorly on the tectum, the temporal field posteriorly, the dorsal field medio‐dorsally, and the ventral field in the latero‐ventral part of the tectum. The projection was found to be essentially linear and uniform with no indication of a specialized area in the visual field in those species investigated. Some receptive fields extended into the anterior binocular visual field.

The larvae ofSiboglinum fiordicumand a reconsideration of the adult body regions (pogonophora)

Abstract Seven larval stages are described. The ciliary rings develop early in ontogeny, are locomo-tory in function and provisional. The dorsal ciliary field develops slightly later and persists in the adult. The posterior constriction develops early and becomes progressively more pronounced. The late larvae show the tentacle rudiment behind which is a ventral furrow bounded by paired glandular papillae. The metasoma has 3 to 4 pairs of setae, and terminates in a sucker which is the organ of attachment for the larva after it has left the parental tube, and is retained in the adult. A variable number of toothed platelets develop early on the mesosoma and persist, and are added to, in the adult. From larval and adult structures the opinion expressed is, that the adult has a small setigerous metasoma, and that the mesosoma is long and secondarily divided into an anterior agonadal and posterior gonadal region.

Noteworthy Records of Skinks (Genus Eumeces) from Northwestern Mexico

Distributional records and taxonomic notes are presented for the following seven species of rare or little-known skinks from the Mexican states of Chihuahua and Durango: Eumeces brevirostris bilineatus, E. callicephalus, E. lynxe durangoensis, E. multilineatus, E. multivirgatus, E. obsoletus, and E. parviauriculatus. E. lynxe durangoensis Tanner is a junior synonym of E. lynxe belli (Gray). E. multivirgatus mexicanus Anderson and Wilhoft is probably a junior synonym of E. multilineatus Tanner. In the collections of reptiles and amphibians made in northern Mexico by summer field expeditions of the University of Kansas Museum of Natural History since 1955, there are some noteworthy specimens of scincoid lizards from Chihuahua and Durango. EUMECES BREVIROSTRIS BILINEATUS Tanner. Data for five specimens from Chihuahua are as follows: KU 44262-3, 15 mi. S and 6 mi. E Creel, 7300 ft., July 16, 1957, and KU 47429, 2 mi. W. Samachique, 7000 ft., July 11, 1958 (juveniles); and KU 51324-5, 2 mi. W. Samachique, 7000 ft., July 11-12, 1958 (adults). The five specimens provide additional information on variation in this recently described subspecies and extend its known range slightly eastward in Chihuahua. The juvenal specimens differ from two juvenal paratypes of bilineatus (KU 44728 and 44730) from the region of El Salto, Durango (paratype from Mojarachic, Chihuahua, not examined), as follows: markings on anterior part of body having greater contrast; dorsolateral lines paler and wider, most distinct anteriorly but easily discernible to insertions of hind limbs; dorsal field between pale lines uniformly metallic, tannish gray (more evident in specimens from Creel than specimen from Samachique); tail bright blue; a distinct, wide, dark stripe on side of body, bordered above by pale dorsolateral line and below by silverish color of belly. Colors of the two adults fall within the range of variation seen in the holotype and four adult paratypes (KU 44726-7, 29, 31-32). One of the adults from Samachique (KU 51324) was giving birth to young when caught;

ON THE DEVELOPMENT OF FEATHERS

SummaryI. Feather papillae are regarded as individually persistent throughout life, from the time of their origin between the sixth and ninth days of embryonic life. In each feather tract the order of origin is significantly related to dynamic field properties of the tract, such as growth rates, degrees of asymmetry, etc.2. Recent work on the anatomy and development of the rhachis with special reference to barb relations and the independent origin of the central rhachis is considered; also the development of the after‐feather and of the pulp and its blood supply.3. By plotting axial growth and isochrones on the vane of the feather it is possible to relate any definitive locus to its time and place of origin in the germ, and hence to the conditions of its determination.4. The papillae of definitive feathers may be transplanted, or subdivided, or parts of papillae of different tracts may be recombined. The results of the operations show that papillae have a definitive bilateral organization, like amphibian eggs, for example; that they are tract‐specific; and that a dorsal field, including the central rhachis, exerts a dominant influence on development. Various abnormalities of feather form produced may be interpreted. Twins and chimaerae may be produced. Abnormalities artificially produced persist through successive generations of feathers from the same follicle. The mesoderm of the papilla is regarded as the seat of the initial inductions.5. The melanophores of feather germs are derived from the neural crest. When transplanted to foreign fowl hosts they determine the donor pattern in the host, as, for instance, barring in a white host. The genotypic composition of the donor melanophore is the controlling factor in both colour and pattern of the host feather in these experiments in all breeds of fowl examined.6. The growing feather germ is a very sensitive indicator; reactions may be read by pattern modifications in the finished feather and referred to their locus of origin in the germ (cf. no. 3).7. The thresholds of reaction of feathers to female hormone increase in proportion to rates of axial growth. This is very conspicuous with reference to the discontinuous rates of different tracts, and is also to be observed with reference to gradations of growth rate within a single tract.8. Within the individual feather germ of breast and saddle tract, threshold of reaction to female hormone and thyroxin rises from dorsal to ventral loci of the collar. These transverse gradients produce transverse patterns on the vane of the feather varying in form according to rise and fall of hormone in the blood stream by absorption and excretion after injection: the principle of rate of reaction which is inversely proportional to threshold is also a factor in the determination of pattern.9. The principles of physiology of development may be applied to some problems of physiological genetics, as, for instance, in the case of barred patterns.

Witaaspis patteni, a New Ostracoderm from the Upper Silurian of Oesel

The genus Witaaspis was erected in 1939 for Pander's Cephalaspis schrenckii (1). In the list of genera and species given in 1939 (2) for the Oesel horizon I listed a second species of Witaaspis. This species, Witaaspis patteni, occurs in the same quarry with Witaaspis schrenckii. Both species are of similar size and body form, but the ornamentation and the form of the median dorsal crista differ sufficiently to make them readily recognizable. Witaaspis patteni is a small form, with a shield length about 17mm., and a breadth of about 20mm. The cornua are rudimentary as in Witaaspis schrenckii. The posterior portion of the shield shows slight segmentation traces. A pronounced median dorsal crista is apparent on most specimens, ending in a median posterior projection which appears to be composed of massed spines or tubercles. The crista is low on Witaaspis schrenckii. The lateral fields are long, ending in front of the cornua. The dorsal field is short, posteriorly truncated, and the endolymphatic apertures are located posterolateral to it. Ridges bound the field laterally. The nasal aperture is long and is located on a slight ridge in the fossa. Its anterior end is wider than its posterior end. The orbits are about 2.5 mm. by 2 mm., and are oval in form. The ornamentation consists of fine tubercles or striae with no separation into fields as in Witaaspis schrenckii. Within the marginal area the tubercles are heavier and massed together. The infraorbital sensory canal is similar to that in Witaaspis schrenckii, but turns medially more abruptly anterior to the nasal fossa.