302 BULLETIN OF THE 



In a stage somewhat later than the mulberry stadium, a section of 

 the embryonic cell-mass — which is grouped about one pole of the egg — 

 shows (Fig. 17) in each cell a nucleus (about which the protoplasm in 

 the figure is shown to have a faintly radiate arrangement), with one or 

 two nucleoli, and numerous cells in process of division (p. 610). Be- 

 tween the cells of uniform appearance there are found a few which 

 differ from them in being smaller, more intensely stained, and in pos- 

 sessing very little protoplasm about the nucleus. Whether these latter 

 are identical with the " cells in process of division," the author does not 

 state. 



Notwithstanding the admitted insufiBciency of his observations on the 

 development of the eggs of the rabbit, Ed. van Beneden ('75, pp. 

 704, 705) believes he may affirm that the supposed [nuclear] vacuoles, 

 which, according to Auerbach, appear in the karyolytic figure during 

 the first segmentation, are not newly formed elements, but fragments of 

 the first embryonic nucleus, which has changed from a spherical to a 

 fusiform condition. They (vacuoles) are bodies formed from nuclear 

 substance ; they become rose-colored in picrocarmine. Each sphere, 

 at the end of the first segmentation, presents a regularly spherical form, 

 and discloses a clear spot composed of two distinct parts. The smaller 

 one, derived from the first embryonic nucleus, is called pronucleus de- 

 rive ; the larger, with a bunched surface, and incompletely enveloping 

 the smaller one, is named pronucleus engendre. The latter is only the 

 remnant of the homogeneous, transparent substance accumulated in the 

 first sphere at the two poles of the first nucleus after the latter has 

 taken the form of a spindle. It is a differentiated portion of the proto- 

 plasm of the cell in process of formation, and presents no genetic bond 

 of connection (lien) with the nucleus of the first sphere. The pronucleus 

 derive grows at its expense, finally absorbing it completely. The '' de- 

 rived pronucleus " thus becomes the nucleus of its vitelline sphere, and 

 contains numerous refringent nucleoli. 



The spheres, some time after division, lose their spherical form, and 

 become mutually flattened, in which state the " pronuclei " have given 

 place to a single nucleus. 



Chapter VI. of this preliminary communication is devoted to cell 

 multiplication. The resume of results from the study of the ectoderm 

 cells, in the case of the rabbit (pp. 732 - 736), do not differ very mate- 

 rially from the results of Biitschli and Strasburger. The first phenomena 

 which announce the approaching division of a nucleus have their seat 

 partly in the nucleus itself, and partly in the body of the cell. The 



