DEVELOPMENT OF ELASMOBRANCH FISHES. 39 



Though they are divided, like the nuclei of the blastoderm, 

 with more or less distinctness into separate areas by a network 

 of lines, their greater size frequently causes them to present an 

 aspect somewhat different from the nuclei of the blastoderm. 

 They are moreover much less regular in outline than these, and 

 very many of them have lobate projections (PL iii. figs. 2a and 

 2c and 3), which vary from simple knobs to projections of such a 

 size as to cause the nucleus to present an appearance of com- 

 mencing constriction into halves. When there are several 

 such projections the nucleus acquires a peculiar knobbed figure. 

 With bodies of this form it becomes in many cases a matter 

 of great difficulty to decide whether or no a particular series of 

 knobs, which appear separate in one plane, are united in a lower 

 plane, whether, in fact, there is present a single knobbed nucleus 

 or a number of nuclei in close apposition. A nucleus in this 

 condition is represented in PI. III. fig. 2 b. 



The existence of a protoplasmic network in the yolk has 

 already been mentioned. This in favourable cases may be 

 observed to be in special connection wdth the nuclei just de- 

 scribed. Its meshes are finer in the vicinity of the nuclei, and 

 its fibres in some cases almost appear to start from them 

 (PI. V. fig. 12). For reasons which I am unable to explain 

 the nuclei of the yolk and the surrounding meshwork present 

 appearances which differ greatly according to the reagent 

 employed. In most specimens hardened in osmic acid the 

 protoplasm of the nuclei is apparently prolonged in the sur- 

 rounding meshwork (PL V. fig. 12). In other specimens har- 

 dened in osmic acid (PI. V. fig. 11), and in all hardened in 

 chromic acid (PL III. fig. 2 a and 2 c), the appearances are far 

 clearer than in the previous case, and the protoplasmic mesh- 

 work merely surrounds the nuclei, without showing any signs of 

 becoming continuous with them. 



There is also around each nucleus a narrow space in which 

 the spherules of the yolk are either much smaller than else- 

 where or completely absent, vide PI. ill. fig. 2 b. 



It has not been possible for me to satisfy myself as to the 

 exact meaning of the lines dividing these nuclei into a number 

 of distinct areas. My observations leave the question open as to 

 wdiether they are to be looked upon as lines of division, or as 



