t 



THE BEGINNINGS OF LIFE. 



205 



\ 



^"n, that the 



rnied' 



av 



\ 



erj 



'um, because 

 id to co-exist 

 arly stage (as 

 1 trace of the 



subsequentlj 

 ivelopment of 



development 

 h the ovisac, 



I 



t 



I 



I 



nt, situated, at a ^ 

 Ti-anukr and ni* 



.e 



\ 



Graafian vesicle ^ 



^ct the foUo^vin? 



these foil* ^^ 

 :.gesizeofabo;^ 



seems 



Id-bearing P 

 r part of the;» 

 I usually Plf , 



to r^ 7 . 

 ,st nottii"6. . ' 



3use jJ"' 

 I-83') 



ov 



Whether or not the first rudiments of the ovum, the 

 (Terminal vesicle, is formed first or formed within the 

 ovisac^ must therefore still be considered an open ques- 

 tion, although the balance of evidence seems^ perhaps, 

 rather more favourable than adverse to its secondary 

 formation ; and if this were the case, the process would 

 strongly resemble that by which the vegetable ovule 

 arises in all flowering plants, 

 the question of the mode of formation of the ovum 

 itself, Dr. Allen Thomson tells us that the earliest 



best traced in such 



Turning, however, to 



stages in its development are 



(t 



I 



Fig. 14. 



Portions of the Ovarian Stroma and Ovisacs of the 



Thrush. (Thomson.) 



a. Earliest state of ova to be perceived in ovarian stroma, consisting, 

 first of minute granular spots ; next of clear points within a granular 

 mass; and thirdly, of small germinal vesicles surrounded by the 

 minutely granular dark yolk-substance. 



h, c. Different stages of formation of the ovisac round the small ova : 

 epithelium is seen to line the sac, and the germinal vesicle, with 

 occasionally a single macula, is now apparent. 



d. The ovisac and ovum in a more advanced stage. 



ov. Ovisac with epithelial lining. 



V. Minutely granular yolk. 



