Equatorial Plate Research Articles

On the Behavior of Chromosomes in the Meiotic Phase of Some Artificially Raised <i>Papaver</i> Hybrids. (With Plate III and one Text-figure)

1. In the prophase of the meiotic division of tile Papaver hybrid, chromosomes forming gemini, unite end to end, not side by side.2. There appear 11 bivalent chromosomes and 10 univalent chromosomes in the first meiotic division. The bivalent chromosomes form the equatorial plate first; all the eleven chromosomes may pass to the anaphase simultaneously, or seven of them first and remaining four afterward; the univalent chromosomes may follow the same process after the halves of the bivalent chromosomes left the equator for the opposite poles of spindle. They make the longitudinal split at the equator and the halves move to the opposite poles.3. The univalent chromosomes, which remained outside the spindle or did not get to the pole before the nuclear membrane appears, are left in the cytoplasm.4. In the second divison of meiosis, the large chromosomes, probably derived from the bivalent chromosomes from the equatorial plate earlier than those from univalent chromosomes. As in first division, some chromosomes derived from the univalent chromosomes are left in the cytoplasm. Some of them remains as isolated chromosomes in the cytoplasm, but some, single or two or more in groups are inclosed by themselves in separate membranes and thus form miniature nuclei.5. As the result of the irregular behavior of the chromosomes, occasionarily two daughter nuclei of the first division of meiosis, connected by a bridge of isolated chromosomes, unite to form a single nucleus. The union of two nuclei, beloning to two different spindles of the second meiotic division, also takes place. The result in the appearance much resemble an amitotic division. Such nuclei form a kind of diploid pollen grains.6. The irregular behavior of chromosomes in the meiotic division, the union of two nuclei, and dropping of certain chromosome cause the abnormalities of pollen grains, not only in shape and size, but also in the combinations of the heredity substances. This may contribute to the origin of the variation or new forms in the offsprings on the one hand, while this may affect the viability of the male gamates and cause the sterility on the other hand.7. F1 plants between Papaver somniferum and P. orientale are more vigorous than their parent plants. The F1 plant appears mostly like P. orientale the _??_ parent, but in some external characters it is intermediate between both parents. The male gamates are mostly sterile.

FURTHER EXPERIMENTS ON THE EFFECT OF HEAT ON THE EGGS OF CUMINGIA

1. If the eggs of Cumingia are subjected to heat immediately after fertilization, they do not form polar bodies. The chromosomes of the first polar spindle divide and two resting nuclei are formed. These nuclei fuse with each other and with the male pronucleus, giving rise to a cleavage nucleus which contains a triploid amount of chromatin.2. The equatorial plates of these eggs show forty-five to sixty chromosomes. About the same number has been found in the cleavage of parthenogenetic (diploid) eggs; but there the individual bodies are smaller than they are in the triploid eggs.3. If fertilized eggs are heated after they have formed polar bodies, the equatorial plates of their first cleavage contain fifty-five to sixty-five chromosomes. These are equal in size to those of a triploid egg.4. Study of later stages (resting nuclei and equatorial plates) shows that the chromatin of the polar nucleus is active, and approximately equivalent to that of a male pronucleus.5. The size and number of the chromosomes in heated eggs is not dependent on the amount of chromatin that is present. They vary with the susceptibility of the egg to heat.6. The conditions described are not in opposition to the theory of the individuality of the chromosomes, if that theory is given a broad interpretation.

Fertilization in Lilium

1. The egg nucleus is in a resting condition when the male nucleus, in spireme stage, comes in contact with it. 2. Distinct male and female spiremes are formed which are segmented into chromosomes while the nuclei are in contact. 3. On the equatorial plate the male and female chromosomes come together in x number of pairs and divide by means of a transverse break, each pair forming 4 segments. The segments move to the poles in pairs. Of the 4x segments formed, 2x go to each pole of the spindle. 4. The chromosomes on the equatorial plate of the second division of the fertilized egg divide longitudinally. 5. The endosperm nucleus divides at least twice before the fertilized egg undergoes division. 6. A distinct spireme is formed in each of the nuclei of the triple fusion, and the 3x segments are oriented on the equatorial plate. 7. The endosperm nucleus divides in the typical vegetative manner by means of a longitudinal splitting of the chromosomes.

AMITOSIS IN CELLS GROWING IN VITRO

The observations above described and the interpretations thereof may be briefly summarized as follows:Amitosis was found to involve only the nucleus and was not a method of cell proliferation. It occurred in normal cells and was characterized by a separation of the nucleus into one or more parts which possessed no reproductive independence.The process of nuclear amitosis consisted in a unilateral or bilateral constriction, manifested by a narrowing of the nucleus in the region of its equator, and a streaming of its contents toward the poles, with final separation of the two nuclear portions. This phenomenon seemed to be associated with the action of the mitochondria and centrosphere upon an elongated nucleus. There was no amphiaster or spireme formation and no centrosome fission. Division of the nucleolus was not an essential. Repetition of this process leads to the formation of a giant cell.Not all nuclei which show elongation and constriction divide by direct fission, but many return to their usual rounded or oval form. When, however, the constriction has passed a critical point the division goes on to completion, and this final stage is rapid.Cells containing nuclei in process of, or the result of, amitosis divide by mitosis. Mitosis in binucleate cells, which are the product of nuclear amitosis, is characterized by the simultaneous appearance in the nuclear parts of a spireme, from which a single equatorial plate of chromosomes is formed. Furthermore, binucleate cells divide as frequently by mitosis as do mononucleate cells, and this was the only form of division found to occur in them.Since the parts of an amitotically divided nucleus do not become separated as reproductive units but divide only by mitosis, in which the chromatin in the parts is recombined, there is nothing in nuclear amitosis opposed to the chromosome hypothesis.The type of amitosis in which the nucleus is split by the growth through it from one side to the other of a membrane was not found. Nuclear figures simulating this proved to be caused by the close apposition of separate nuclear sacs, or by nucleoli, mitochondria or folds of the nuclear membrane.The dyes, janus green and gentian violet, were toxic and their presence in the cell was incompatible with its continued life. They were, however, of service in quickly studying structural details which were not discernible in the living state.Nuclear fragmentation, which differs in many ways from nuclear amitosis, is a pathological condition, and occurs in degenerating cultures.It is believed that the facts brought to light through the tissue culture method may be applied to the interpretation of the phenomena of normally developing cells.

The Relation between Chromosomes and Sex-determination in “Abraxas grossulariata.”

IN a paper on this subject in the Journal of Genetics (vol. iv., June, 1914, p. 1) I gave evidence that in a strain of A. grossulariata which I have bred for several years two kinds of eggs are produced, having respectively twenty-eight and twenty-seven chromosomes. Since the somatic chromosome-number is fifty-six in the male and fifty-five in the female, it seemed evident that the eggs with twenty-eight were male-determining, those with twenty-seven female-determining. In this strain some families in each generation consist entirely of females, so it was hoped to prove the correctness of the conclusion with regard to sex-determination by finding that in families consisting entirely of females all the eggs contain twenty-seven chromosomes. I have now examined the eggs of several such families, and find, contrary to expectation, that the equatorial plate of the inner polar spindle contains twenty-eight chromosomes about as frequently as twenty-seven. The new material confirms the observation that twenty-seven occur in one spindle and twenty-eight in the other, but it seems to make it certain that the presence of twenty-eight chromosomes in the inner spindle does not necessarily cause the production of a male—at least, in the strain which produces all-female families. A possible explanation of the anomaly is that in all-female families a chromosome is eliminated at a later stage, but at present I have no direct evidence for this. I have material preserved in the hope of testing this suggestion, but the investigation is likely in any case to be a lengthy one, and circumstances may prevent my continuing it for some months. I therefore make this short statement of the facts as at present known, in order that it may not be assumed that the existence of male and female-determining chromosomes has been finally demonstrated in Abraxas.

The effect of carbon dioxide on the eggs of Ascaris

The undivided eggs of Ascaris megalocephala (var. bivalens) were kept in an atmosphere of carbon dioxide for three months. On the removal of the eggs from the gas, a few smears were allowed to undergo full development. Only about one third of the embryo, were normal, the remainder being either masses of disorganized cells, or embryos in which the posterior end was differentiated, together with the primordial germ cells. The problem was to determine the causes of the abnormalities. Eggs were preserved in all stages, stained and mounted in toto. The first of these was the fusion of the chromosomes in the equatorial plate phase of the dividing S1-blastomere. (This is the “Ur-somatic” cell in which the diminution process takes place.) The fusion resulted in one of two things: (a) When the fusion involved the greater part of all the chromosomes, the blastomere did not divide. At the next division cycle, a tetraster appeared with eight chromosomes (or their equivalents in small “diminished” chromosomes) lying in the spindles. The tetraster divided very irregularly and the result was the total disorganization of the cells of the ectoderm. Such eggs gave rise to embryos which failed to invaginate. (b) When the fusion involved the ends of the chromosomes only, then division took place, but the chromatin was unequally distributed to the two daughter blastomeres, A and B. This led to an upsetting of the cleavage rhythm of these two cells, the blastomere with less chromatin dividing more rapidly than its mate. The P1 blastomere (the cell which gives rise to the cells of the entoderm, mesoderm, the stomadeum cells, and the primordial germ cells) and its derivatives divide normally throughout development.

Societies and Academies

EDINBURGH. Royal Society, June 19.—Prof. Bower, F.R.S., vice-president, in the chair.—M. Jules Cardot: Les Mousses de 1'Expédition nationale antarctique ecossaise. These were collected in various localities visited, and included a number of new species and genera.—Dr. J. Aitken, F.R.S.: Some nuclei of cloudy condensation. Some years previously the author, when enumerating the dust particles in the air at certain regions of the West Highlands remote from centres of population, had noticed from time to time a sudden, and at first inexplicable, increase in the number of dust particles. A recent study of the phenomenon had shown that the increase was due to the sunning of the material on the foreshore of neighbouring islands and coasts. The paper discussed the probable causes of this production of dust particles, and described a number of experiments on the direct effect of sunlight upon various substances.—Dr. A. A. Lawson: Nuclear osmosis as a factor in the mechanism of mitosis. A study of the spore mother-cells of Disporum, Gladiolus, Yucca and Hedera, and the vegetative cells in the root tip of Allium, has revealed a series of stages in the development of the mitolic spindle which has hitherto been overlooked. They are important and critical stages concerning the fate of the nuclear membrane, and are to be found in the early pro-phase, preceding the organisation of the equatorial plate. Contrary to the generally accepted view, it has been found that the nuclear membrane does not break down during spindle formation, but behaves as a permeable plasmatic membrane should behave under varying osmotic conditions. The interpretation of these stages throws an entirely new light on the problem of the “mechanism of mitosis,” and necessitates a revision of the accepted views of nuclear phenomena. It goes to prove that osmotic conditions are active factors in the formation of the acromatic spindle.— Dr. A. G. M'Kendrick and Dr. Kesava Pai: The rate of multiplication of micro-organisms: a mathematical study. Assuming the law that the rate of increase of fast-growing organisms is proportional to the number of organisms present and to the concentration of the foodstuff, the authors express this in the mathematical form dy/dt=by(a—y). At the beginning, y is small compared with a, so that the constant ab is equal to the rate of change of log y. From the graph which gives log y in terms of time, the value of ab may be readily obtained, and from the indications of the experiments the limit a towards which y tends may be inferred. The quantity also gives by a simple calculation the period of a generation. The numbers calculated from the integrated expression were found to be in good agreement with the numbers obtained by direct measurement.

The Spermatogenesis of Stenobothrus viridulus; with Special Reference to the Heterotropic Chromosome as a Sex Determinant in Grasshoppers.

The Spermatogenesis of Stenobothrus viridulus; with Special Reference to the Heterotropic Chromosome as a Sex Determinant in Grasshoppers.

The chromosomes in cross-fertilized Echinoid eggs

This paper deals with observations made on sections of cross-fertilized eggs of two kinds: (1) Toxopneustes eggs fertilized with Moira sperm, (2) Arbacia eggs fertilized with Moira sperm.The results of the study may be summarized as follows:1. The equatorial plate of the Moira-Toxopneustes cross shows a mixture of two kinds of chromosomes not sufficiently unlike one another to enable a positive distinction between the two.2. The equatorial plate of the Moira-Arbacia cross shows a mixture of two kinds of chromosomes, one variety long, the other variety short. These differences in form are correlated with the spermatozoon and the egg respectively.

THE FEMALE CHROMOSOME GROUPS IN SYROMASTES AND PYRROCHORIS

The conditions seen in Syromastes marginatus L. are of inter est on account of the light that they throw on those observed by Morgan in Phylloxera, as reported by him at the December meet ing of the American Society of Zoologists, and recently published in the issue of Science for Feb. 5, I9o9. In both forms the “? accessory― chromosome is not a single but a double body, and the female chromosome-groups contain two more chromosomes than the male. A reexamination of the spermatogenesis of Syromastes' led to a confirmation of Gross's result that the spermatogonial number is even (22), and that the “? accessory― chromosome is formed by the union of two chromosomes that are separate in the sperma togonia. This double element divides equationally in the first spermatocyte-division but passes undivided to one pole in the second, so that half the spermatozoa receive two more chromo somes (12) than the other half (io). This led me to the infer ence that the female somatic groups should have two more chromosomes than the male—i. e., 24 instead of 22, as had been described by Gross. I had at that time no female material, but through the kindness of Professor Boveri have since obtained an abundant supply of the ovaries. Examination of this material demonstrated the correctness of my earlier inference. A consid erable number of ovaries have been sectioned, many of which contain numerous and very fine division-figures, showing the chromosomes with great clearness. Whenever a good view of the equatorial plate can be obtained, 24 chromosomes are unmis takably seen to be present, as is clearly shown in photographs. Two figures (Fig. i, c, d) are appended, both of which were drawn upon enlarged photographs by the method described in my fourth “? Study.― Syromastes is an exceptionally favorable form

THE CHROMOSOMES IN CROSS-FERTILIZED ECHINOID EGGS

This paper deals with observations made on sections of cross-fertilized eggs of two kinds: (1) Toxopneustes eggs fertilized with Moira sperm, (2) Arbacia eggs fertilized with Moira sperm.The results of the study may be summarized as follows:1. The equatorial plate of the Moira-Toxopneustes cross shows a mixture of two kinds of chromosomes not sufficiently unlike one another to enable a positive distinction between the two.2. The equatorial plate of the Moira-Arbacia cross shows a mixture of two kinds of chromosomes, one variety long, the other variety short. These differences in form are correlated with the spermatozoön and the egg respectively.

AN INTRA-NUCLEAR MITOTIC FIGURE IN THE PRIMARY OÖCYTE OF A COPEPOD, CANTHOCAMPTUS STAPHILINUS JUR

Next article FreeJournal ArticlesAN INTRA-NUCLEAR MITOTIC FIGURE IN THE PRIMARY OÖCYTE OF A COPEPOD, CANTHOCAMPTUS STAPHILINUS JURROBERT W. HEGNERROBERT W. HEGNER Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The Biological Bulletin Volume 14, Number 6May 1908 Published in association with the Marine Biological Laboratory Article DOIhttps://doi.org/10.2307/1535867 Views: 50Total views on this site © 1908 Marine Biological LaboratoryPDF download Crossref reports no articles citing this article.

On the occurrence of heterotypical mitoses in cancer

The present paper refers to a communication* made to the Royal Society in January, 1904. In that paper and its expansion, published later, we emphasised the significance of the zoological distribution of cancer ; we discussed the unique features of the processes responsible for the experimental transmission of carcinoma from one animal to another and the limitations to its successful attainment: we also published a series of figures depicting the characters of the nuclei of cancer cells during division, in the malignant new growths of fishes and mammals. We shall we give a different explanation of the mitoses We figured in our earlier communications as resembling the heterotypical mitoses of reproductive tissue. We have found that those mitoses may be interpreted as somatic mitoses with longitudinally split chromosomes. Their apparent heterotypical form is thus due to variations in the development of the achromatic figure, the peculiar form of the chromosomes and their mode of attachment to the spindle. Our figures of heterotypical mitoses in cancer confirmed the observations of Farmer, Moore and Walker, communicated to the Royal Society at the preceding meeting, but we dissociated ourselves from their conclusions on the diagnostic value and the significance of the phenomenon. The amount of chromatin entering into the equatorial plate of the dividing cells of human cancer had long been known to be subject to diminution (von Hansemann, 1893), but the presence of heterotypical mitoses appeared to throw a new light on its occurrence and meaning.