2o6 THE BEGINNINGS OF LIFE. 



animals as the thrush, the yellow-hammer,, or the 

 chaffinch on account of the transparency of the 

 ovarian tissue in these smaller singing birds. He 

 describes the earliest appearances in the ovarian stroma 

 of the thrush to be as follows : first, the appearance ' of 

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

 minute granular mass ; and third, of small germinal 

 vesicles surrounded with the minutely granular dark 

 yolk-substance/ Afterwards the ovisacs are said to 

 form around the rudimentary ova. Here again, therefore, 

 we meet with mere granules or molecules as the first 

 representatives of the future ova. These molecules, 

 however, appear to belong to the yolk, whereas in the 

 Nematoid ovarian tube those which first appeared were 

 representatives of the future germinal vesicles. Even 

 Dr. Allen Thomson, who is quite indisposed to believe 

 that cell elements can spring up de novo^ is yet neverthe- 

 less compelled to make the following statement concern- 

 ing the origin of the germinal vesicle, the potential part, 

 as he and others believe, of the egg itself: c The manner 

 of the very first origin of the germ of the ovum is still in- 

 volved in obscurity, for we only know of the existence of 

 an ovi-germ when the germinal vesicle has attained an 

 appreciable size. Whence the first germs of the germinal 

 vesicle proceed can as yet be matter o?tly of conjecture. . . . 

 Here observation fails, and we are lost in the region of 

 speculation.' It is open therefore for us to presume that 

 an aggregation of granules, such as he himself describes 

 and figures as occurring in the thrush, may be the very 



