[97] EMBRYOGRAPHY OF OSSEOUS FISHES. [tfA 



gerraiual i)rutoplasm, which takes it up by iutiissnsception aud apposi- 

 tion. The coarser granules of the deutoplasm are slowly broken down, 

 as we saw in the ca.se of Alosa, and converted into tlie more homogene- 

 ous and much more finely granular and more highly vitalized protoplasm 

 of the yelk hypoblast. 



In the very act of the mechanical dissociation of the i)rotoplasm of 

 the egg from its deutoplasm, we have an explanation of why the nuclei 

 are attracted to the former aud repelled from the latter. The first is 

 the portion of the egg which is dynamic in character, the portion in 

 which developmental potentiality inheres ; the second is in the static 

 condition of what Beale might perhaps call "formed material." This 

 attraction of the nucleus or germinative vesicle for the i)rotoplasin of 

 the egg points to its true nature, and must be of a directive or trophic 

 character, as insisted upon by Rauber; its office, in short, appears to 

 be to direct those phenomena of protoplasmic rearrangement and con- 

 tractility, and perhaps of metabolism, which transpire during segmen- 

 tation. The rhythmical metamori)hosis of the nuclear bouies into com- 

 plex "asters" or caryokiuetic figures, with granular lines radiating in 

 all directions through the surrounding plasma, like the pseudopods of 

 a heliozoon, would seem to indicate that something of this sort is the 

 function of a part, at least, of the nucleus. 



The first segmentation furrow, or that usually described as such, 

 which divides the germinal disk of the Teleostean ovum into two halves, 

 is, according to Hoffmann's investigations, not the first, but, on the 

 contrary, must be considered as the second to be developed in the order 

 of time. His researches have shown that a cleavage spindle is devel- 

 oped, when the germinal disk is finally marked off from the yelk hypo- 

 blast, just after impregnation. The axis of this spindle also coincides 

 with the diameter of the egg. We therefore have, in this fact, the final 

 proof of the law of nuclear displacement, which has been pointed out 

 a little way back, and also why it is that there may be a great dis.simi- 

 larity in the size of the deutoplasmic, as comi)ared with the protoplasmic 

 mass of germinal matter, dependent as this must be upon the amount 

 of food yelk which has been stored in the ovum during its intrafollicular 

 development. 



Inasmuch as the yelk of some ova has the form of coarse ovoidal 

 bodies, involved in a matrix of soft plasma, as in those of Lepidosteus 

 and Amia, for example, an approach is evidently made towards the 

 condition of the stored nutrient materials in the cells of seeds. As in 

 the latter, we may call these bodies, which are said to be composed of 

 ichthyine by chemists, globoids. Upon making sections of the mature 

 ovarian ova of Lejndotitcus, I find that the germinative vesicle has left 

 the center of the egg and passed outwards almost into contact with the 

 egg-membrane. Here the nucleus is surrounded by a mass of germinal 

 matter evidently destined to form the germinal pole; of the egg. The 

 coarse globoids of the central and lower portions of the egg gradually 



