Posterior Daughter Research Articles

X-Ray-Induced Delay of Cell Division in Synchronized Tetrahymena pyriformis

X-Irradiation delays division of heat-synchronized Tetrahymena pyriformis (a ciliate protozoon) if exposure occurs prior to a critical time after the end of the synchronizing treatment (EST). Exposure after this critical time does not significantly delay the first synchronized division but does delay the second. The time of the transition from a state where the cells are delayed to one where they are not is somewhat dose dependent: within limits, the larger the exposure, the later is the transition time. The division delay response is always correlated with a resorption of the oral primordium of the presumptive posterior daughter cell. The amount of time for resorption varies with the time after EST at which the cells are irradiated and is dose dependent. The data are consistent with the hypothesis that irradiation produces damage during all parts of the synchronized cell cycle, but that, depending on the dose and the time of irradiation after EST, the damage may or may not trigger a response that leads t...

Phase Contrast Microscopy of Cytoplasmic Organelles in the Gymnostome Ciliate Chlamydodon pedarins

SYNOPSIS.Chlamydodon pedarius has peculiar and interesting cytoplasmic organelles, such as the pharyngeal basket and the cross‐striped band, and exhibits plasmotomy of an uncommon type at the division stage. For comparison of the results of observations on fixed and stained material and on living material examined with phase contrast, and because of finding important differences in such a comparison, this morphological study of the cytoplasmic organelles was undertaken.The cilia, arranged in about forty rows only on the ventral surface, the anterior part of which shifts out of the dorsal body, bending to the dorsal side, are almost the same everywhere, about 5 μ in length. The cross‐striped band, encircling the body surface so as to divide it into dorsal and ventral parts, has the power of movement, such as folding of the semicircular trichites and closing or opening of them. The oral apparatus, composed of a membranous system and a pharyngeal basket, is an elaborate organelle. The membranous system shows such movement as seen in a sphincter muscle, moving the triangular trichites in a manner which opens or closes the cytostome. Each of the triangular trichites is con nected with the expanded end of a long trichite; together these structures. 11–13 in number, constitute the pharyngeal basket. The ridges, the long trichites and the semicircular trichites are composed of fibrillar elements, but their twisted figures may be produced artificially by staining methods.Binary fission of Chlamydodon pedarius, under natural conditions in the season from April to October, occurs daily during the period 11 a.m. to 4 p.m. Each of the fissions takes about 2 hours. In the first half of this fission time: the V‐area consisting of four central ciliary systems gives rise to transitions in the arrangement of the ciliary rows and ridges on both its anterior and middle portions; the pharyngeal basket falls down into the cytoplasm; and rosettes appear in the above two fields. On the other hand, plasmotomy arises in a fission furrow from the right side of the fission line. In the second half of the fission process, the oral apparatuses develop from the rosettes, while the old basket is dissolved into the cytoplasm; and, as the fission furrow extends leftward, two transverse bands and the frontal pellicle of the posterior daughter ciliate are organized on the surface of the fission furrow.

Some Observations on the Morphology and Division of Balantidium coli and Balantidium caviae (?)

SYNOPSIS. Studies of the body ciliature of Balantidium coli and B. caviae (?) after Breslau's opal‐blue and Klein's silver nitrate techniques revealed a preoral‐dorsal suture area where some of the ciliary rows fail to reach the peristomial margin. The incomplete kineties ranged up to a dozen in number and were variable in arrangement. In a count of 100 specimens of B. caviae (?) the incomplete kineties were at the right of the suture in 39, at the left in 24 and on both sides of the suture line in 37. At the posterior end not many kineties reach the pole but no sutural pattern was seen in that region. Scattered irregularities in the ciliary rows were sometimes seen.Studies of the oral region tend to confirm the view of Fauré‐Fremiet that the peristomial ciliature consists of short rows of cilia which are continuations of the anterior body kineties. Membranelles were not found. Thus, some species of Balantidium, at least, show affinities with the Holotricha in agreement with Nie and Fauré‐Fremiet.Fission commonly produces two equal‐sized daughters but many cases of unequal division were observed. In both these species conjugants are much smaller than vegetative animals and two preconjugant divisions are indicated, the first of which may be unequal.During the early stages of fission, the anterior ends of the kineties of the posterior daughter change direction, becoming oblique in the fission zone. In this region the kinetosomes multiply; possibly some of the kineties also divide but evidence for this is incomplete. No evidence of reorganization at the anterior end of the anterior daughter was seen.Attempts to infect hamsters with B. coli and B. caviae (?) failed. No parasites were found in two collared peccaries repeatedly examined.

The Binary Fission of Lacrymaria olor (O.F.M., 1786).

SUMMARY. Observations on binary fission of Lacrymaria olor show that it is a transverse fission. It involves probable intranuclear division of the micronucleus. Both micro‐ and macronucleus elongate in preliminary stages. Each is ultimately divided as cytoplasmic constriction cuts the spindle fibers of the former, and the connecting, nucleoplasmic thread of the latter.Surging movements of cytoplasm after fission elongate the daughter organisms and move new nuclei to normal, central sites. The anterior proboscis of the posterior daughter regenerates suddenly, complete with coronal cilia. Metachronal waves along ciliary meridians, strongly reversed on the posterior daughter, cause an oscillating movement which pulls the two apart, except for a slender, pellicular thread, ultimately severed. Until broken, this thread connects the rear tip of the anterior animal to the forward end of the proboscis of the posterior one. The organism is semi‐quiescent, with proboscis retracted (except spasmodically) throughout fission. After fission the anterior animal quickly begins feeding movements and soon swims away. The posterior animal requires about half an hour before being able to begin feeding and swimming movements.The anterior contractile vacuole of the original animal becomes the primarily active vacuole of the anterior daughter; the posterior one that of the posterior daughter. Missing vacuoles are regenerated by the daughters in about one hour after fission. The division process requires about one hour for completion at 22.4°C.

Observations on the Morphology and Division of Eudiplodinium neglectum Dogiel (Ciliata Entodiniomorpha) from the Stomach of a Moose (Alces americana).*

SUMMARY. The material containing the ciliate Eudiplodinium neglectum Dog. from the rumen of a moose was fixed with 4% formalin solution and studied both unstained and after staining with methylene blue or methyl green.This ciliate is closely related to Eudiplodinium neglectum Dog. (1925) formae spectabile Dog. (1925) and impalae Dog. (1925), but differs from them in the presence of a transverse cuticular line. The form of the macronucleus of the investigated ciliates is regularly elongated clavate, the anterior end being wider than the posterior one. The following measurements were obtained from 14 specimens: length 81.3 μ (67.2–112 μ), width 66.2 μ (48.8–84 μ).During division the anterior daughter gets the old skeletal plate and a new one arises de novo in the posterior daughter. The anlage of a new skeletal plate for the posterior daughter was observed in earlier and later telophases, first as an indistinct structure, later as a group of a variable number of granules, more often about 30. This anlage gradually grew into a typical skeletal plate. The anlage of the pharynx in the posterior daughter was seen in later telophases. A part of the distal end of the old skeletal plate (one, two or five rectangular prisms belonging to this organelle) and a part of the distal end of the old oesophagus are possibly cut off during division and dissolved in the protoplasm of the posterior daughter. A crossing of the distal end of the old skeletal plate by the division plane was observed only in those specimens in which this part consisted of one row of the rectangular skeletal prisms and was not found in the specimens with a shaft of the skeletal plate consisting of two rows of polygons. In later division stages a bending of the old skeletal plate takes place.The morphological plasticity of the skeletal plate (loss of the distal part and subsequent bending of this organelle during the division of the ciliate) observed by the present writer and its dynamic reversibility (disappearing during starvation and thickening under satisfactory feeding conditions, reported by Westphal) confirm the assumption that the skeletal lamina functions primarily as a storage organelle. Some cases of destruction and defective development of the old skeletal plate were observed.The presence of fat in some specimens of E. neglectum Dog. is noted.

The Common Occurrence of Micronuclear Variation During Binary Fission in an Unusual Race of Paramecium caudatum

Unstable micronuclear behavior was investigated in an unusual race of Paramecium caudatum. Lines were begun, after isolating single vegetative specimens, to yield mass cultures. After study of living specimens in the precision micro‐compression chamber and permanent preparations stained with Feulgen and iron‐hematoxylin, most paramecia revealed a single micronucleus but many were observed with two micronuclei and fewer with more than two micronuclei—occasionally three, rarely four. Specimens measured 225 microns in length; the micronucleus about seven microns. Instead of normal cyclosis, the protoplasm exhibited great fluidity. Generally two contractile vacuoles were present but specimens with three vacuoles, even four, were not uncommon.The method of producing amicronucleate specimens and those with variable numbers of micronuclei was discovered by studying large numbers of actively dividing paramecia. Instead of a micronucleus passing to each daughter at the end of fission as in normal animals, the entire late telophase stage of the dividing micronucleus is passed to the anterior or posterior daughter cell at the time of constriction of the cell. The result is that one daughter is bimicronucleate and the other daughter amicronucleate. Bimicronucleate and amicronucleate animals are capable of dividing normally. In bimicronucleate specimens, division stages show two micronuclei in late telophase stages that result in four micronuclei, two passing to each daughter cell. However, aberrations may again occur in fission to produce variations in number of micronuclei. The irregularly shaped, atypical, macronucleus may extrude chromatin or may undergo complete fragmentation (hemixis, type D). Paramecia and macronuclei may be parasitized by a microorganism which may cause this derangement of normal micronuclear events. This possibility of induction of micronuclear variation in Paramecium by foreign microorganisms may be of considerable evolutionary significance in the genus.

Memoirs: The Neuromotor System of Euplotes patella during Binary Fission and Conjugation

1. The neuromotor system of Euplotes patella Ehrenberg was studied in different stages of the life-cycle, including the adult, and asexual and sexual reproduction. 2. In the adult the basal granules of all the cirri are arranged in straight primary and secondary rows. The fibrils from the bases of the cirri are in general parallel with either the primary or secondary rows of basal granules of the cirri to which they are attached. This is interpreted as an indication of the evolution of the organism from an ancestor with a simple neuromotor system in which the cilia were uniformly distributed over the surface of the body in longitudinal, slightly spiral rows. 3. The basal apparatus of a bristle consists of a basal granule at the bottom of a depression in the ectoplasm which is surrounded by a group of rodlets and ends at the surface in a ring connected with the polygonal system. The polygonal or silverline system is pellicular in position. 4. During asexual reproduction the entire set of cirri is resorbed and replaced by two new sets of cirri, one for each daughter. One frontal cirrus for the anterior daughter develops in the old peristomial field of the parent, while the corresponding cirrus for the posterior daughter develops in the new peristome. The right marginal cirri arise on the dorsal surface along the rows of bristles and later move to the ventral surface. The fibrils develop outward from the bases of the cirri. 5. During binary fission a new peristome arises in a depression in the ectoplasm independently of the old peristome. The old peristome remains in the anterior daughter without at the time undergoing any visible change in structure. 6. The multiplication of the bristles is limited to a zone on either side of the future plane of constriction. Multiplication occurs by a series of fissions of the basal granules in this area. Dedifferentiation of bristles was not seen. 7. The polygonal system is replaced over the entire surface of the body with the exception of the old peristomial field. The new system originates in many separate loci in connexion with the bristles on the dorsal surface, and with the rudiments (Anlagen) of the cirri and peristome on the ventral surface. 8. During conjugation there are two successive reorganizations of the neuromotor system, that of the ‘gamete’ (conjugant) and that of the zygote. 9. The first reorganization, that of the gamete, begins during the maturation divisions preparatory to fertilization. During this reorganization the posterior portion of the peristome is resorbed and the remaining anterior portion is later replaced. The eighteen cirri are replaced by a set containing only seventeen cirri. 10. The second reorganization, that of the zygote, occurs during the differentiation of the nuclei in the exconjugants. It involves the completion of the peristome by differentiation of the missing posterior portion, and the replacement of the set of seventeen cirri by a complete set of eighteen cirri. 11. These protoplasmic reorganizations, invariably associated with both asexual and sexual reproduction, involve a structural and presumably a physiological rejuvenation resulting in the possibility of an indefinitely continued existence of the individual in the Protozoa. It may be that sexual reproduction is not necessary to bring about this result, but further work on the relationship of endomixis to the problem is needed.

Division and conjugation in Nyctotherus cordiformis (EHr.) Stein (Protozoa, Ciliata) with special reference to the nuclear phenomena

AbstractA cytological study of the complete life cycle of Nyctotherus cordiformis (Ehr.) Stein, a heterotrichous ciliate from the large intestine of tadpole and adult Hyla versicolor hosts is presented. In division a partial dedifferentiation of parental ingestatory structures occurs, then redifferentiation, to be retained by the anterior daughter. For the posterior daughter, the ingestatory apparatus arises de novo. In conjugation, two ciliates fuse along their peristomes. The macronucles undergoes complete fragmentation while the micronucleus divides three times. The first pregamic division results in two micronuclear products; the second division, four micronuclear products, three of which degenerate. The remaining product enters into the third pregamic division to produce the two functional, migratory and stationary, pronuclei. Interchange of migratory pronuclei follows at the fused anterior ends of the conjugants to form the amphinucleus which divides once to produce the micronucleus and the macronuclear anlage. Development and behavior of the unusual macronuclear anlage (‘spireme‐ball’ of Stein and Schneider) is described for the first time. At the end of the conjugation process, ingestatory structures of each conjugant completely dedifferentiate while a complete new set arises de novo posterior to the old ones. In this case, conjugation occurs only in tadpoles which are metamorphosing into frogs. Conjugation here is interpreted as an effort made by the ciliates to overcome a physiological crisis during the drastic host transformation changes.