-68 THE STRUCTURE AND DEVELOPMENT 



than the one last described, about which it may be well to say a 

 few words before proceeding to the further development of the 

 permanent ova. 



The younger of these ovaries was from a Scyllium embryo 10 

 centimetres long, preserved in osmic acid. 



A considerable number of nests were present (PI. 24, fig. 13), 

 exhibiting, on the whole, similar characters to those just 

 described. 



A series of measurements of the nuclei in them were made, 

 leading to the following results : 



0-014 mm. 

 o'oi4 mm. 

 O'oi6 mm. 

 o - oi6 mm. 

 o'oiS mm. 

 o'oiS mm. 



Thus, if anything, the nuclei were slightly smaller than in the 

 younger embryo. It is very difficult in the osmic specimens to 

 make out clearly the exact outlines of the various structures, the 

 nuclei in many instances being hardly more deeply stained than 

 in the protoplasm around them. The network in the nuclei is 

 also far less obvious than after treatment with picric acid. The 

 permanent ova were hardly so numerous as in the younger ovary 

 before described. A number of these were measured with the 

 following results : 



Ovum. Nucleus. 



ox>3 mm. .;.... 0-014 mm - 



0-034 mm o'oiS mm. 



0-028 mm o - oi6 mm. 



0-03 mm o'02 mm. 



0-04 mm 0'02 mm. 



0-04 mm o - o2 mm. 



0-048 mm 0'02 mm. 



These figures shew that the nuclei of the permanent ova are 

 smaller than in the younger embryo, and it may therefore be 

 safely concluded that, in spite of the greater size of the embryo 

 from which it is taken, the ovary now being described is in a 

 more embryonic condition than the one last dealt with. 



Though the permanent ova appeared to be formed from the 

 nests in the manner already described, it was fairly clear from 



