ON THE EMBRYOLOGY OF THE TELEOSTS. 193 



A description of the changes undergone by a single egg will be given in detail while the 

 variations presented by others will be noticed as occasion demands. At the close of the 

 section on segmentation, a tabulated account of a few eggs, all apparently of the same 

 species, will be found, with the periods of time occujjied in the various phenomena of 

 segmentation. 



This egg with two blastomeres when first placed under the microscope had nuclei in 

 each cell, though, judging from the analogies presented by the later stages as well as by 

 the eggs of Merlucius at the same period of development, the nuclei probably did not 

 reappear until some minutes after the first segmentation furrow was completed. Soon 

 after this the nuclei disappeared, and in six and one half minutes afterwax'd they were no 

 longer visible, the first external features of cell division were noticed. A slight furrow 

 appeared in the surface of each blastomere, their direction being at right angles to the 

 original plane of segmentation (fig. 13). At first these furrows existed only at the junc- 

 tion with the primary one and were also superficial. They then gradually extended out- 

 wards and downwards from this place until in thirty seconds from their first appearance 

 they had completely separated each blastomere into two. Two minutes later the nuclei 

 reappeared. 



In some eggs, between the completion of the segmentation furrow and the reappearance 

 of the nuclei in the four resulting blastomeres, marked amoeboid movements were observed. 

 In other eggs from the same lot these movements were not noticed until the blastoderm 

 had eight blastomeres. These amoeboid motions were very marked and similar ones were 

 noticed in connection with each segmentation from the third onward. It is difficult to 

 describe or illustrate these motions. Processes were sent out by the cells, and furrows 

 appeared cutting into the blastomeres, conveying the impression, the first time that the 

 phenomenon was witnessed, that the cells were about to divide again immediately without 

 the reappearance of the nuclei or the intervention of the usual period of rest. On the 

 contrary, with the reappearance of the nuclei, or very soon after, these motions ceased 

 and the blastomeres acquired their regular cellular appearance and an interval of rest inter- 

 vened before further cell division begun. 



As was mentioned above, the same amoeboid movements were witnessed at each seg- 

 mentation and in all eggs studied, and, though we are by no means positive, it seemed to 

 us that connected with these movements was an increase in the amount of protoplasm and 

 that particles of the yolk or deutoplasm were taken into the blastoderm. Certain obser- 

 vations which we made, but which are not easy to describe, seemed to admit of this and 

 only this interpretation ; and the fact that the blastoderm grows, not only in superficial 

 extent, but also in volume, shows that the amount of protoplasm is in some way increased 

 and thus adds additional weight to the view which we have taken. On the other hand 

 the fact that the cells, after they have reached a quiescent state and have regained their 

 usual smooth contours, exhibited no traces of globules or granules of yolk as would have 

 been expected with bodies of such different refractive indices, would seem to be against 

 this idea. It may be, however, that the deutoplasm undergoes a gradual change, and that 

 portions of it are transformed into the substance of the intermediary layer and that the 

 nourishment of the cells is in turn derived from the intermediary layer. That this inter- 



MEMOIKS BOST. SOC. NAT. HIST. VOL. III. 25 



