OF THE VERTEBRATE OVARY. 569 



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 primitive 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 o - oi6 mm., and the nucleus 

 croi2 mm. Isolated ova with metamorphosed nuclei could 

 also be found measuring O'O22, and their nuclei about 0*014 mm. 

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

 somewhat more advanced than the ovary in which the formation 

 of permanent ova was at its height. Fewer permanent ova were 

 in the act of being formed, and many of these present had reached 

 a considerable size, measuring as much as O'oy mm. Nests 

 of the typical forms were present as before, but the nuclei in them 

 were more granular than at the earlier period, and on the average 

 slightly smaller. A series measured had the following diameters : 



cro i mm. 

 0-012 mm. 

 o - oi4 mm. 

 o - oi6 mm. 



One of these nests is represented on PI. 25. fig. 20. Many 

 nests with the outlines of the individual ova distinct were also 

 present. 



On the whole it appeared to me, that the second mode of 

 formation of permanent ova, viz. that in which the nest does not 

 come into the cycle of development, preponderated to a greater 

 extent than in the earlier embryonic period. 



POST-EMBRYONIC DEVELOPMENT OF THE OVA. My investi- 

 gations upon the post-embryonic growth and development of 

 the ova, have for the most part been conducted upon preserved 

 ova, and it has been impossible for me, on this account, to work- 

 out, as completely as I should have wished, certain points, more 

 especially those connected with the development of the yolk. 



Although my ovaries have been carefully preserved in a large 

 number of reagents, including osmic acid, picric acid, chromic 

 acid, spirit, bichromate of potash, and Muller's fluid, none of 

 these have proved universally successful, and bichromate of potash 



B. 37 



