400 F. M. BALFOUR. 



fig. 13), exhibiting, on the whole, similar characters to those 

 just described. 



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

 leading to the following results : — 



0-01 i mm. 

 0-014 mm. 

 016 mm. 

 OOIG mm. 

 0-018 mm. 

 0-018 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 per- 

 manent ova were hardly so numerous as in the younger ovary before 

 described. A number of these were measured with the following 

 results : — 



Oviim. Nucleus. 



0-03 mm 014 mm. 



0-034 mm O'OIS mm. 



0-028 mm O'OIG mm. 



003 mm 0-02 mm. 



04 mm 002 mm. 



0-04 mm 0-02 mm. 



0-048 mm 0-02 mm. 



These figures show that the nuclei of the permanent ova are 

 smaller than in the younger embryo, and it may thertfore 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 ap})eared to be formed from the 

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

 the sections of this ovary that many of the original primitive ova, 

 after a metamorphosis of the nucleus and without coalescing 

 with other primitive ova to form nests, become converted directly 

 into the permanent ova. Many large masses of primative ova, 

 or at least of ova with the individual outlines of each ovum 

 distinct, were present. The average size of ova composing these 

 was how^ever small, the body measuring about 0-016 mm., and 

 the nucleus 001:i mm. Isolated ova with metamorphosed nuclei 

 could also be found measuring 0-022, and their nuclei about 

 0-OM. mm. 



The second of the two ovaries, hardened in osmic acid, was 

 somewhat more advanced than the ovary in which the formation of 

 p.T'jaaneiit ova was at its height. Fewer permanent ova were in 



