CHAPTER I. 

 THE RIPE OVARIAN OVUM. 



THE ripe ovum is nearly spherical, and, after the removal 

 of its capsule, is found to be unprovided with any form of pro- 

 tecting membrane. 



My investigations on the histology of the ripe ovarian ovum 

 have been made with the ova of the Gray Skate (Raja batis) 

 only, and owing to a deficiency of material are somewhat im- 

 perfect. 



The bulk of the ovum is composed of yolk spherules, 

 imbedded in a protoplasmic matrix. Dr Alexander Schultz 1 , 

 who has studied with great care the constitution of the yolk, 

 finds, near the centre of the ovum, a kernel of small yolk sphe- 

 rules, which is succeeded by a zone of spherules which gradually 

 increase in size as they approach the surface. But, near the 

 surface, he finds a layer in which they again diminish in size 

 and exhibit numerous transitional forms on the way to molecular 

 yolk-granules. These Dr Schultz regards as in a retrogressive 

 condition. 



Another interesting feature about the yolk is the presence 

 in it of a protoplasmic network. Dr Schultz has completely 

 confirmed, and on some points enlarged, my previous observa- 

 tions on this subject' 2 . Dr Schultz's confirmation is the more 

 important, since he appears to be unacquainted with my pre- 

 vious investigations. In my paper (loc. cit.\ after giving a 

 description of the network I make the following statement as to 

 its distribution. 



1 Archiv fur Micro. Anat. Vol. XI. 1875. 



' 2 Quart. Journ. Micro- Science, Oct. 1874. [This edition, No. V.] 



