II 



MEIOSIS IN THE FEMALE 59 



The particular problems raised by the germinal vesicle stage in 

 oogenesis are : 



(i) The continuity of the chromosomes throughout this period. 



(2) The relation between the chromosomes and the nucleoli. 



(•3) The connection between the peculiar germinal vesicle stage and 

 the synchronous enormous growth of the cytoplasm of the egg, together 

 with the formation of yolk. 



(4) Does any comparable stage occur in spermatogenesis ? 



(i) The Continuity of the Chromosomes 



The conditions in the germinal vesicle have been urged against the 

 theory of the genetic continuity of the chromosomes, since in some species 

 the fully developed germinal vesicle — which it must be remembered is 

 interposed between syndesis and metaphase I. — shows no trace of 



Fig. 23. 



A chromosome from the geriiiiual vesicle of Pristiurus. (After Riickert. A. A., 1892.) 



chromosomes. This condition occurs, for instance, in many Echinoder- 

 mata, whose fully developed germinal vesicle consists of an enormous 

 nucleolus suspended in a fine, very faintly staining, reticulum in which 

 no trace of individual chromosomes can be detected. 



As in the case of the resting stage between two ordinary somatic 

 mitoses, however, we must ascribe the invisibility of the chromosomes in 

 such germinal vesicles to their extreme diffusion and loss of staining 

 power, and not to any loss of identity. This can be clearly determined 

 by a comparative study of this period of oogenesis. In the Copepoda 

 (a group which has been extensively studied in this connection) we 

 find a great range of variation in the degree of certainty with which 

 the chromosomes can be recognized throughout the growth period {e.g. 

 Matschek, 1910). In -Cyclops gracilis the chromosomes remain sharply 

 individualized throughout, as is also the case in Hetcrocope saliens 

 (Fig. 24). In Diaptomus castor, however (Fig. 25), the chromosomes 

 become very diffuse at the height of the germinal vesicle stage, and their 



