Maturation Division Research Articles

THE FORMATION OF GIANT POLAR BODIES IN CENTRIFUGED EGGS OF ILYANASSA

1. If the second maturation spindle of the egg of Ilyanassa is displaced from the animal pole by centrifugal force, a giant polar body may be formed. If the sperm nucleus is included in the giant polar body the latter, instead of the egg proper, may develop.2. The close of the maturation division in centrifuged and elongated eggs is attended by the production of clusters of cytoplasmic lobes around the region where the achromatic figure lay. These lobes are distinct from the normal polar lobe.3. In strongly centrifuged eggs five zones of substances are separated. These include two clear zones separated by a band of fine, colorless granules.

Parthenogenesis in the Ovaries of Guinea Pigs

It is not a new thing to find segmenting eggs in the ovaries of guinea pigs. Loeb (1912) described structures in the ovaries of guinea pigs which he said he thought were the result of parthenogenetic development. In 1923 he said, A relatively far-going parthenogenetic development of eggs in the ovary of a guinea pig has been observed by us so far in thirty animals. It can therefore not be considered an exceptional occurrence. Again (in 1932) he described four cases and further stated that the number observed had increased to forty-five. In most cases these were of animals which had been used for experimental purposes. He had had some on starvation diet and others he had injected with one or another hormone. However, he described one case which occurred in one of his control animals. Courrier and Oberling (1923), Courrier (1923), Branca (1925), Lelievre, Peyron, and Corsy (1927) have observed structures similar to those which Loeb has observed, but in each case it was in pathological individuals. Squier (1932) said that Mrs. Lewis had found one egg dividing parthenogenetically among those which she was observing in tissue culture. In our combined work on the normal embryology of the guinea pig we have sacrificed over two hundred mothers. These mothers have been in various stages of pregnancy from seven days to almost term. Besides these we have killed a great many nonpregnant females. All of these animals had been kept under as favorable conditions as we could provide and the food was as nearly a normally balanced ration as we knew how to prepare. The food was the same as that which has been used in the genetic experiments carried on by Doctor Ibsen. In fact, the grain mixture already combined was obtained from Doctor Ibsen. We supplemented this with straw, alfalfa hay and either fresh alfalfa or sprouted oats. We preserved the ovaries of the greater number of these animals. In addition to these ovaries we have had the ovaries of a number of the guinea pigs which we have fed on a limited diet. Now we have been devoting some time to the examination of these ovaries. Up to the present time more than fifty of the ovaries from animals having normal food have been examined, and in every ovary, without exception, we have found eggs within Graafian follicles either in the polar body formation or in various stages of segmentation or both. The polar body formations are in almost all stages. Some are in a metaphase of the first polar spindle while others are clearly in the process of the second maturation. In these evident cases of second polar body formation the first polar body is seen attached to the egg. The segmenting eggs range from the two-celled stage to a wellformed morula. The maturation divisions are easily distinguished from the segmentation divisions. The maturation spindle is small and near the periphery of the egg, while the segmentation spindle, when present, is in the center of the cell. The length of the spindle is determined by the size of the cell. There is practically no rhythm in segmentation and the morula is composed of cells of various sizes. In a previous paper, Harman and Brill, 1933, we mentioned finding polar spindles in eggs of vitamin-C deficient animals. Our

Insect development. VIII. Maturation and early development of unfertilized grasshopper eggs

AbstractMaturation and early cleavage in unfertilized Melanoplus differentialis eggs have been followed with material secured immediately before as well as after oviposition, and (1) fixed at once, or (2) held in an incubator at 25°C. and, subsequently, fixed at selected intervals. Eggs ready to be laid were all found in the metaphase of the first maturation division. The second polar body is given off (at 25°C.) within 5 to 7 hours after laying. Meiosis appears to be unaffected by the absence of the sperm nucleus and proceeds at the same rate as in fertilized eggs. No morphological differences could be found between the process here and in eggs from mated females.During early cleavage, or later, the diploid number of chromosomes may be restored in some (or perhaps all) cells of the embryo.Development begins in the greater number of these unfertilized eggs but is successfully completed in only a very few.

Chromosome Numbers in Xiphophorin Fishes

The fishes of the genera Platypoecilus and Xiphophorus constitute the tribe Xiphophorini. The six species of xiphophorin fishes may be regarded as geographical species as they occupy distinctive drainage areas in Mexico. The chromosome numbers in males of all the species of the tribe Xiphophorini were determined at the first maturation division in males. In Platypoecilus couchianus, P. xiphidium and P. maculatus, and in Xiphophorus hellerii and X. montezumae the haploid number of chromosomes is twenty-four. In P. variatus the haploid number is twenty-five, the additional univalent chromosome appearing smaller than the bivalents. The chromosomes of F1 hybrids between P. variatus and P. maculatus are described. The extra chromosome may, together with another variatus chromosome, associate with a maculatus chromosome to give a trivalent, or it may remain unpaired as a univalent. The chromosomes of these species are small and the complements they form are quite similar in appearance. Therefore no cytological ...

Studies on the spermatocyte divisions in ascaris megalocephala; with special reference to the central bodies, Golgi complex and mitochondria

AbstractThe centrioles are recognized early in the prophase of the primary spermatocyte. They soon become double and migrate around the nucleus in opposite directions. As this is completed the nuclear membrane breaks down and spindle fibers appear. The centrioles divide in the metaphase at a time when the centrosome is still perfectly spherical. The centrosome divides in the anaphase, giving the two centers for the second division. The centriole disappears in the spermatid and cannot be seen in later stages. The behavior of the centers during the spermatocyte divisions is strikingly like that of the egg centers and other types of mitoses. Therefore, it is concluded that the centrioles of the spermatocytes are not to be regarded as different from the centrioles in other types of mitoses.The Golgi bodies increase in number and size during the growth period of the cell. They are usually found in the shape of rings. From these rings are produced the refringent granules which fuse in the late spermatid to form those of the mature sperm. It is therefore concluded that this process represents the formation of the acrosome. The mitochondria show little change during the maturation divisions. In the late spermatid they aggregate around the nucleus and become vesiculated. This is interpreted as the formation of the prenebenkern.

On the Number of Chromosomes and the Type of Sex-chromosomes in Man

1. The spermatogonia of a Japanese man show forty-eight chrcmosomes. But it is difficult to locate the unpaired chromosomes X and Y in the spermatogonial chromosome-complex. The serial arrangement is of no service, as is illustrated by the example of Trixalis nasuta in which the chromosomes are much larger in size and much fewer in number than in man.2. In the first maturation division the chromosomes are twentyfour in number. The sex-chromosome and twelve large tetrads encircle the Small ones so as to form a rosette in the metaphase of the first division.3. The sex-chromosome is composed of two heteromorphous elements, a long and a short rod. It lies at the periphery of the equatorial plate in the normal condition. Sometimes it is displaced into the centre of the equatorial plate by the effects of the fixation. There is no evidence that the sex-chromosome is of V-shape as reported by Oguma et Kihara, and Winiwarter et Oguma.4. The X and Y elements conjugate lineally in the first meiosis as is the Gase in all mammals. This mode of conjugation has been reported by Minouchi as asymmetrical synapsis.5. These elements separate in the first meiosis; as a result, one of the daughter cells receives the X-element and the other the Y-element, so that in the metaphase of the second division each of the germ-cells contains twenty-four chromosomes.

Spermatogenesis in gecko japonicus (dumeril and bibron)

AbstractThe nuclear changes involved in the two maturation divisions of G. japonicus have been studied in considerable detail. All observations compel a telosynaptic interpretation. The duality, an apparent parasynapsis, as seen beginning from synizesis up to diplotene is a result of a longitudinal splitting of the chromosomes joined end to end. Strepsinema is brought about by breaking up of the diplotene thread into segments, which really are pairs of synaptic mates in end‐to‐end union; each segment then bends at its middle to form V‐ or ring‐tetrads. There are altogether twenty tetrads. All chromosomes assume a rod shape when in the metaphase plate. A pair of heterochromosomes was observed to be slower than the rest in assuming the rod shape and in getting into the plate. The marching of the synaptic mates toward their respective poles is asynchronous. Second division begins right after the chromosomes have reached the poles. Zwischenkörper observed at the end of the second division are regarded as formed by the granules seen in the polar regions during the first division.

Maturation Divisions inTradescantia, Rheo and Oenothera

Maturation Divisions in<i>Tradescantia</i>, Rheo and Oenothera

Maturation Divisions in Tradescantia , Rheo and Oenothera

Maturation Divisions in <i>Tradescantia</i> , Rheo and Oenothera

A cytological study of affects of ultra-violet light on the egg of Nereis limbata

A. Three chief facts are established: 1. In the egg of Nereis limbata inseminated after exposure to ultraviolet light, due to the failure of the first maturation spindle to move, the maturation divisions are endoplasmic with the result that the egg possesses four ovotid nuclei. 2. The union of the four ovotid nuclei with the sperm nucleus gives rise to a pentaploid zygote nucleus from which a bipolar spindle bearing seventy chromosomes, five times the haploid number, emerges. 3. The cytoplasmic inclusions do not show the segregation which in the normal egg takes place during the period before first cleavage. That is, the normal cytoplasmic flow is inhibited. B. It is held that this inhibition is due to the affect of ultra-violet light on the egg's cortex.

A HAPLOID PLANT IN &lt;i&gt;PORTULACA GRANDIFLORA&lt;/i&gt; HOOK

1. The gametic chromosome number in the normal Portulaca grandiflora is 9 as already stated by TJEBBES, and the somatic number is 18 (Fig. 18).2. Two haploids were found among 168 F2 interspecific-hybrids (Magenta No. 22×Orange No. 35) in 1931, next year one haploid was obtained from 100 F3 plants. Their parents were normal morphologically and cytologically. These haploids are of about half the stature of P. grandiflora with all organs proportionally smaller.3. There are 9 univalents in the first maturation division of P. M. C.. The 9 univalents are separate in the possible assortment of 1 and 8, 2 and 7, 3 and 6, 4 and 5 (Tab. 1). Sometimes 1-3 lagging chromosomes are observed (Figs. 2-5).4. In the homotypic division the halves of dyad chromosomes are distributed with the result that four nuclei are formed all lacking whole set of chromosomes. Accordingly the pollen grains, which are shrunken and empty, have no function (Figs. 6-10, Tab. 2). As far as the present investigation goes, I could not find the assortment of 0 and 9. This assortment is however possible in rare case.5. Haploid selfed gave no seed at all, and also pollination experiment with the haploid on normal plants was negative, but its reciprocal cross gave 5 seeds. One of them gave a progeny almost wholly of parent type, and has diploid chromosome number of P. grandiflora. This fact apparently indicates that the non-reduction of chromosomes happened in maturation division of E. M. C. of the haploid plant.

CHROMOSOMES OF ARTIFICIALLY ACTIVATED EGGS OF URECHIS

1. The embryos resulting from the artificial activation of Urechis eggs are diploid in chromosome number. 2. The diploid number is apparently obtained by the utilization of the first polar spindle for the first cleavage and the substitution of a mitotic division for the second maturation division.

The Maturation Divisions and Fertilization in Eggs of Sciara Coprophila: Lint

The Maturation Divisions and Fertilization in Eggs of Sciara Coprophila: Lint

Microsporogenesis and Embryogeny in Certain Species of Bromus

1. Bromus marginatus and B. rubens are octoploid and tetraploid respectively; B. villosus is variable between octoploid and decaploid. 2. Polyploidy and other irregularities in the maturation division indicate that these species may be hybrids. 3. Lagging bivalents are found in B. villosus and B. marginatus. An irregular homeotypic division, showing much lagging and extrusion, occurs in B. villosus. 4. Varying types of chromatin extrusion are found in all three species, together with polycary and sterile pollen. 5. No examples of cytomyxis were observed. 6. Megasporogenesis and embryo sac development appear to be rather typical for the Gramineae. 7. Antipodals generally vary in number from five to eight, with a maximum of ten seen in one instance. Their nuclei are large, are often organized into cells, and finally occupy a lateral position just below the center of the sac, in which position they undergo dissolution, after an existence considerably longer than that characteristic of smaller cells.

Some cytoplasmic structures in the male reproductive cells of a pseudoscorpion (Chelanops corticis)

AbstractThe chondriosomes of the germinal epithelium are vesicular, whereas the Golgi material takes three forms. The aggregation of chondriosomes about the Golgi cap, located on the nucleus, suggests a chemical interchange between these in the growth period. They become cylindrical as the Golgi cap moves from the nucleus and becomes spherical. It is at this time joined by other Golgi material. The entire aggregation is dispersed previous to the maturation divisions, where the inclusions studied are only approximately equally divided, in contrast to conditions in the true scorpion, Centrurus exilicauda. Golgi granules on chondriosomal surfaces in the spermatid again suggest chemical interchange. The later changes of chondriosome vesicles to discs, and back to spheres, may be means of regulating chemical reaction. A close relation between chondriosomes and Golgi material is indicated by various bodies, of Golgi origin, within the former in the spermatid. A thick thread finally originates from among the chondriosomes of the elongated sperm. Spiral threads surrounding the elongating nucleus arise from reunited Golgi material, a derivative of this substance not previously recorded. The acrosome, also of Golgi origin, undergoes several changes in shape and shows several parts. The elongated nucleus, spiral thread of Golgi origin, acrosome, chondriosomal thread, and unusually long axial filament become coiled and encysted in an oval mature sperm capsule. In the female duct the sperm uncoils.

Studies on Reptilian Chromosomes III

1. For the fixation of metaphase chromosomes in all cell generations CHAMPY's mitochondrial fixative, concentrated 1.5 time as strong as the original, is found to be the most adequate one.2. The basal chromosome number of the male of Eumeces latiscutatus is 26. The spermatogonial chromosomes can be sorted into two categories, macro- and micro-chromosomes. The macro-chromosomes are 12 V-shaped ones and the micro-chromosomes are 14 short rodand dot-like chromosomes.3. Through maturation divisions every resultant spermatid contains a haploid set of chromosomes which consists of 6 V-sphaped and 7 dot-like ones.4. The 12 V-shaped macro-chromosomes of this lizard probably correspond to macro-chromosomes of other members of the family Scincidae, e. g. Seincus officinalis and Chalcides tridactylus, but as to the relation between the 14 micro-chromosomes of the former and the 12 micro-chromosomes of the latter, nothing can be said definitely.5. The sex-chromosomes of this lizard are two short rod-like ones. Between the members of the sex-chromosomes there is no differente by which one can distinguish the one as X and the other as Y. Consequently, this lizard has sex-chromosomes of an isomorphic type.6. If we substitute X for the sex-chromosome the chromosome complex of the male may be formulated as 24+X+X=26.

The spermiogenesis of Succinea ovalis say, with special reference to the components of the sperm

AbstractAn investigation of the spermiogenesis of Succinea ovalis Say, a small terrestrial pulmonate, has revealed: 1) The germ cells are differentiated from indifferent germinal epithelial cells. In this form the germinal epithelium is a true epithelium, and not a syncytium. 2) Forty chromosomes are found in the spermatogonial divisions and twenty in the maturation divisions. 3) Early in spermiogenesis the proximal centriole penetrates through the spermatid nucleus and, with the oxychromatin, forms an intranuclear rod similar to that reported for certain prosobranches. The homology and significance of the rod are discussed. 4) Of the cytoplasmic structures, the mitochondria and the Golgi apparatus were followed through all stages of spermatogenesis. 5) At the maturation divisions the mitochondria are grouped into peculiar. thread‐like structures. Some of the mitochondria take part in the formation of the sheath around the axial filament of the spermatozoon, while the remainder are sloughed off with the cytoplasmic remnant. 6) The Golgi apparatus consists of a number of banana‐shaped rods closely grouped around the idiosome. Three to five Golgi rods are found in the spermatid stages. A portion of the Golgi apparatus and idisome (acroblast) forms the acrosome, and the Golgi remnant is discarded at the end of spermatogenesis. 7) In mature sperm both head and tail have a spiral structure. The origin and nature of the spirals are pointed out.

The Oogenesis of Calanus finmarchicus

ABSTRACT Three regions can be recognized in the ovary: a multiplication zone containing oogonia undergoing mitosis, a synapsis zone containing the first formed oocytes in the prophases of the maturation division, and a growth zone containing oocytes in a series of growth phases with the nucleus in a ‘resting condition ‘. The oogonial nuclei contain two or three nucleoli—plasmosome and karyosomes. In the oocytes a single nucleolus is present; this is formed by the fusion of the plasmosome and at least one karyosome and is therefore an amphinucleolus. The chromatin in the oogonia and young oocytes is arranged round the periphery of the nucleus andis aggregated in knots (pp. 196-200). Nucleolar extrusion begins in the young oocyte and continues throughout the growth period. It is most marked in the young oocytes and in oocytes about to undergo maturation (pp. 200-3). In the older oocytes the chromatin is in the form of a tangled thread surrounding the nucleolus. Immediately before maturation this condenses and circular chromosomes emerge: these form tetrads (pp. 203-5). The mitochondria are present in the oogonia and very young oocytes in the form of a cap lying upon the surface of the nuclear membrane. The mitochondrial elements spread and multiply until they surround the nucleus as a ring; afterwards they disperse and are distributed evenly throughout the cytoplasm. They swell up and finally yolk-droplets appear in their place (pp. 207-11). Yolk-formation usually begins in half-grown oocytes, but is sometimes earlier. The formation of yolk-droplets begins at the periphery of the cell and proceeds inwards. It is suggested that yolk is formed by transformation of the mitochondria and the deposition in them of substances derived from the cytoplasm and the nucleolus. The cytoplasm is flocculent in the young oocytes, granular in the half-grown oocytes, and filled with fluid vacuoles in mature oocytes. It passes from a primary condition of oxyphily to basophily and finally back to a secondary oxyphil condition in mature oocytes (pp.211-13). In the young oocytes deeply-staining spherical structures were seen adjacent to the mitochondrial cap. From their appearance it is possible these bodies represent the Golgi apparatus, but Da Fano fixation failed to demonstrate them. In half-grown oocytes the apparatus was visible in the complex condition at one side of the cell. As growth proceeds it passes from a complex to a diffuse condition and in mature oocytes the Golgi elements are uniformly distributed throughout the cytoplasm (pp. 213-15).

Studies on Reptilian Chromosomes II

1. For the fixation of metaphase chromosomes in all cell generations CHAMPY's mitochondrial fixative, concentrated 1.5 time as strong as the original, is found to be the most adequate one.2. The basal chromosome number of the male of Eumeces latiscutatus is 26. The spermatogonial chromosomes can be sorted into two categories, macro- and micro-chromosomes. The macro-chromosomes are 12 V-shaped ones and the micro-chromosomes are 14 short rodand dot-like chromosomes.3. Through maturation divisions every resultant spermatid contains a haploid set of chromosomes which consists of 6 V-sphaped and 7 dot-like ones.4. The 12 V-shaped macro-chromosomes of this lizard probably correspond to macro-chromosomes of other members of the family Scincidae, e. g. Seincus officinalis and Chalcides tridactylus, but as to the relation between the 14 micro-chromosomes of the former and the 12 micro-chromosomes of the latter, nothing can be said definitely.5. The sex-chromosomes of this lizard are two short rod-like ones. Between the members of the sex-chromosomes there is no differente by which one can distinguish the one as X and the other as Y. Consequently, this lizard has sex-chromosomes of an isomorphic type.6. If we substitute X for the sex-chromosome the chromosome complex of the male may be formulated as 24+X+X=26.

The cytology of several species of iceryine coccids, with special reference to parthenogenesis and haploidy

AbstractFour species of iceryine coccids have been studied cytologically in connection with certain breeding experiments. These are Icerya littoralis, Icerya montserratensis, Echinicerya anomola, and Crypticerya rosae. For the three first‐named species the complete chromosomal history has been established, and the evidence on the fourth, Crypticerya rosae, is sufficient to indicate that it differs in no essential respect from the others. The following résumé may, therefore, be considered to apply to all four species. The females are diploid, with a chromosome number of four, and the males are haploid, with a chromosome number of two. Oogenesis proceeds quite normally; two tetrads are formed and two maturation divisions occur in which the chromosomes are reduced to two in each female pronucleus. All eggs undergo this reduction: if the eggs are then fertilized, the diploid number is thus restored and development into females ensues; if the eggs remain unfertilized, whether in the body of a virgin or of a fertilized female, they develop parthenogenetically, with no restoration of diploidy, into haploid males. The spermatogenesis of the haploid males involves a single meiotic division, demonstrably equational in character; the accompanying cytoplasmic division is suppressed, and from each of the binucleate spermatids thus produced two spermatozoa are formed. These conditions are contrasted with the functional hermaphroditism and haploid parthenogenesis of Icerya purchasi.