THE GAMETES IN PLANTS AND ANIMALS 



347 



gametic cells. The only conclusion in agreement with the facts 

 is that the gametes are physiologically integral parts of the 

 organism, that they are, like other parts of the organism, more or 



m 





Gft 



188 



190 



191 



FIGS. 187-191. Oogenesis of ascidian and fish: Fig. 187, ovotestis of young bud 

 of Distaplia (ascidian) with primitive egg cell, o; Fig. 188, growing egg with test 

 cells and follicle; Fig. 189, portion of half-grown egg, showing follicle, test cells, and 

 formation of yolk (from Bancroft, '99); Figs. 190, 191, Two stages in the growth 

 and differentiation of the egg of Rhombus (fish) (from Cunningham, '97). 



less highly differentiated cells, and that, like other parts, they 

 undergo differentiation because of the conditions to which they 

 are subjected in the organism and not because of peculiar, inherent 

 properties. 



