Albert Tyler

THE PRODUCTION OF NORMAL EMBRYOS BY ARTIFICIAL PARTHENOGENESIS IN THE ECHIUROID, URECHIS

1. The eggs of Urechis may be activated by hypotonic solutions ranging from distilled water to 80 per cent sea water, and trochophores indistinguishable from those produced by fertilized eggs may be obtained.2. The time of exposure necessary to bring about activation increases with increased concentration of sea water.3. The activated eggs may extrude two, one or no polar bodies. When the exposure is such as to produce 100 per cent activation, two polar bodies are extruded on practically all the eggs, but to either side of this optimum exposure the proportion of activated eggs with no polar bodies increases. Eggs with one polar body occur in small numbers, and the single polar body is equal in size to the two polar bodies of the normal egg.4. Only the eggs with no polar bodies divide and form embryos. Those with two polar bodies or with one polar body may sometimes produce uncleaved swimmers.5. The eggs which extrude no polar bodies show a very poor response in other respects to the treatment. The eggs wh...

THE POINT OF ENTRANCE OF THE SPERMATOZOöN IN RELATION TO THE ORIENTATION OF THE EMBRYO IN EGGS WITH SPIRAL CLEAVAGE

If the entrance of the spermatozo6n into the egg is instrumental in determining the planes of cleavage, and the cleavage planes bear a definite relation to the embryonic axes, it would still remain important to find out whether the side of the egg on which the sperm enters is a factor in locating the dorsal (or ventral) side of the embryo. In some eggs having an equal first cleavage, such as the frog, the ascidian and the sea-urchin, observations of this kind have been reported, and a distinct relation has been found between the side of the egg on which the sperm enters and the future dorso-ventral axis of the embryo. Curiously enough, despite the large number of careful observations on the cell-lineage of eggs with a spiral type of cleavage, there is only one set of observations on the relation of the entering point to the first cleavage plane, and even here we do not know whether the side on which the sperm enters becomes the dorsal or the ventral side. In the course of our work another relation was found that is both novel and has a bearing on the interpretation of the so-called law of alternate rightand left-cleavage in spiral types. In Cumingia it was discovered that two types of second cleavage occur in equal numbers, one of which in ordinary parlance would be called a right-handed, the other a left-handed spiral, yet in both cases the third cleavage was found to be always dexiotropic. As a consequence of this relation it follows that in one case the first plane of cleavage corresponds to the median plane of the embryo, and in the other case the second plane of cleavage corresponds to the median plane, provided the later sequence of events is the same for both types. A third relation has not, so far as we know, been carefully studied, namely, whether in eggs with an unequal first cleavage, the plane of cleavage passes through the pole or consistently to the side. Without exception our observations show that the plane passes to the side on

ON THE ENERGETICS OF DIFFERENTIATION. III

It has been concluded from earlier work (Tyler, 1933, 1935) that energy is required for the processes of embryonic differentiation, although the quantities involved could not be estimated. As part of a program to evaluate the energy requirements, an investigation of the temperature coefficients of the rate of development and of the rate of respiration was undertaken. This involved the determination of the temperature coefficients for cleavage for comparison with that of differentiation. In the previous work distinction was made between the maintenance, growth and differentiation processes of development. Cell division was left out of account. This was justified inasmuch as it did not enter as a factor in the results. In the cases of both the half-embryos and the giant embryos gastrulation occurs when the original egg has undergone the same number of cell divisions as it normally does. This was shown in the early work of Morgan (1901, 1903), Driesch (1900) and Bierens de Haan (1913). In considering the effect of temperature on development there is, of course, the possibility that cleavage and differentiation may be affected differently. That would mean that the embryos in the same stage of differentiation would contain different numbers of cells if reared at different temperatures, provided, of course, that the later divisions have the same temperature coefficient as the earlier ones. The data that exist in the literature in regard to this point are of two sorts, namely, that in which estimates of the number of cells present in embryos of the same stage, but raised at different temperatures, are

ON THE ENERGETICS OF DIFFERENTIATION, VI COMPARISON OF THE TEMPERATURE COEFFICIENTS OF THE RESPIRATORY RATES OF UNFERTILIZED AND OF FERTILIZD EGGS

1. The effect of temperature on the rate of oxygen consumption of unfertilized and fertilized eggs of Urechis, Strongylocentrotus, Ciona and Dendraster was investigated.2. The unfertilized eggs exhibit a rising rate of respiration with time in allfour species. The rise is much more rapid in Strongylocentrotus and in Dendraster than in Urechis and in Ciona. This rise appears to be correlated with the loss of fertilizability on the part of the eggs.3. Methods of determining the temperature coefficients in such a way as to take into account the general rise (which is a significant factor in prolonged runs) and other variations are described.4. Only the temperature coefficients for the same temperature intervals are compared, the respiration being determined at two temperatures in each experiment. With Urechis and with Strongylocentrotus eggs, experiments were run at temperatures between 22° and 5°; with Ciona, between 25° and 12°; and with Dendraster, 22° and 12°. The experiments with Urechis and Strongyloce...

ON THE ENERGETICS OF DIFFERENTIATION

1. Giant embryos produced by the fusion of two fertilized eggs develop more rapidly than normal sized embryos.2. The bearing of this result on the energetics of differentiation is discussed.3. A new method of fusing eggs is described.

ON THE ENERGETICS OF DIFFERENTIATIONp VIIc COMPARISON OF THE RESPIRATORY RATES OF PARTHENOGENETIC AND FERTILIZED URECHIS EGGS

It has been long been known that the rate of respiration rises during development. This increase in rate is evidently not directly proportional to the increase in the number of cells (cf. Needham, 1931). It might, nevertheless, depend upon changes in the egg brought about by cell division, so that when cleavage fails to occur the rise in respiration would be inhibited. We have considered in previous work the dependence of the form-changes on the respiration, the rate of oxygen consumption being taken as a measure of the energy available for the various developmental processes. We consider now the possibility that the developmental changes determine in turn the rate of respiration. If, for example, early cleavage is inhibited in a manner that does not affect the absolute rate of respiration at the particular stage, then we may expect, on this basis, failure of the subsequent rise. In the early work of Warburg (1910) it has been shown that cleavage could be suppressed in sea urchin eggs by means of phenylurethane without immediately affecting the respiratory rate. However, the question of whether or not the rate would rise later was not investigated. Also it has been shown that after parthenogenetic activation of sea urchin eggs the same increase in rate occurs that is obtained normally upon fertilization (Warburg, 1910; Loeb and Wasteneys, 1913). But here again it would be desirable to know what happens later, especially since the parthenogenetically activated eggs develop much more slowly in general and often stop in early cleavage or even fail to divide.

POLAR BODY EXTRUSION AND CLEAVAGE IN ARTIFICIALLY ACTIVATED EGGS OF URECHIS CAUPO

1. Urechis eggs activated by prolonged exposure to ammoniacal sea water give a high percentage of cleavage as Hiraiwa and Kawamura showed, but such exposures also give a high percentage of polar body suppression.2. Isolation of eggs of known polar body history shows that practically all those eggs divide that fail to extrude the first or the first and second polar bodies, but only a small percentage of those eggs that extrude the first and second polar body.3. Eggs that fail to extrude the first polar body may produce two, one or no polar bodies at the time when the second polar body should appear. Later, two, three or four nuclei are visible in the egg corresponding to whether two, one or no polar bodies are present. The first cleavage of these three types gives two, three or four cells respectively.4. Eggs that extrude the first polar body almost invariably produce the second.5. Determinations of the time of polar body appearance after various lengths of exposure indicate that not more than four or five...

ON THE ENERGETICS OF DIFFERENTIATION. IV: COMPARISON OF THE RATES OF OXYGEN CONSUMPTION AND OF DEVELOPMENT AT DIFFERENT TEMPERATURES OF EGGS OF SOME MARINE ANIMALS

It has been assumed (Tyler, 1933, 1935) that energy is required for the differentiation as well as the maintenance and growth processes of development and that this energy is supplied by reactions involving oxygen. The terms maintenance, growth and differentiation have been used in various ways by different investigators. By maintenance I mean the processes by which the egg or embryo is kept alive in a resting condition. An unfertilized egg illustrates this. Also a fertilized egg in which development has been reversibly stopped would illustrate maintenance. But it cannot be assumed that the maintenance energy requirement of a developing egg is equivalent to the metabolism of an unfertilized or of a fertilized egg in which development has been stopped, for the maintenance requirement of a fertilized egg is probably different from that of an unfertilized egg; it very likely changes throughout development and under different conditions. In other words, it takes different amounts of energy to keep different kinds of cells alive under the same conditions, and the same kind of cell alive under different conditions.

PRODUCTION OF CLEAVAGE BY SUPPRESSION OF THE POLAR BODIES IN ARTIFICIALLY ACTIVATED EGGS OF URECHIS

1. The polar bodies can be suppressed in artificially activated eggs of Urechis by means of a second treatment with dilute sea water.2. The treatment must be applied before the time of extrusion of the first polar body and continued until after the time of extrusion of the second.3. The eggs in which the polar bodies are thus suppressed undergo cleavage whereas ordinarily they would not do so.4. Similar second treatments applied after the time of the extrusion of the second polar body do not induce cleavage.

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.