DEVELOPMENT OF THE ELASMOBRANCH FISHES. 65 



actually the case. In my account of the segmentation I have, 

 indeed, already mentioned this, and I will return to it, but 

 before doing so will enter more fully into the distribution of 

 these nuclei in the yolk. 



They appear in small numbers around the blastoderm at 

 the close of segmentation, and round each one of them there 

 may at this time be seen in osmic acid specimens, and 

 with high powers, a fine network similar to but finer than 

 that represented in PL 3, fig. 2. This network cannot, as 

 a general rule, be traced far into the yolk, but in some 

 exceptionally thin specimens it may be seen in any part of 

 the fine granular yolk around the blastoderm, the meshes of 

 the network being, however, considerably coarser between than 

 around the nuclei. This network may be seen in the fine 

 granular material around the germ till the latest period of 

 which I have yet cut sections of the blastoderm. In the later 

 specimens, indeed, it is very much more distinctly seen than 

 in the earlier, owing to the fact that in parts of the blastoderm, 

 especially under the embryo, the yolk-granules have disap- 

 peared partly or entirely, leaving only this fine network with 

 the nuclei in it. 



A specimen of this kind is represented in PI. 3, fig. 2, 

 where the meshes of the network are seen to be finer 

 immediately around the nuclei, and coarser in the intervals. 

 The specimen further shows in the clearest manner that this 

 network is not divided into areas, each representing a cell and 

 each containing a nucleus. I do not know to what extent this 

 network extends into the yolk. I have never yet seen the 

 limits of it, though it is very common to see the coarsest yolk- 

 granules lying in its meshes. Some of these are shewn in 

 PL 3, fig. 2,yk. 



This network of lines 1 (probably bubbles) is characteristic of 

 many cells, especially ova. We are, therefore, forced to believe 

 that the fine granular and probably coarser granular yolk of 

 this meroblastic egg consists of an active organized basis with 



1 The interpretation of this network is entirely due to Dr Kleinenberg, who sug- 

 gested it to me on my shewing him a number of specimens exhibiting the nuclei and 

 network. 



B. 5 



