80 PETER OKKELBERG 



the presence or absence of oocytes. The presence of large cysts 

 of indifferent germ cells has been taken to be a male charac- 

 ter, the whole cyst being homologous to an oocyte with its fol- 

 licle; but to a certain extent the male character remains obscure, 

 since it is not until the animal approaches the sexually mature 

 condition that the male germ cells can be identified as such. The 

 presumably male germ cells of the larger cysts continue to divide 

 until after metamorphosis, but the cells resulting from each divi- 

 sion are, for a long time, not essentially different from the pri- 

 mordial germ cells. The only secondary characters that distin- 

 guish the adult male are the long, slender urogenital papilla and 

 the absence of an anal fin, but these do not appear until after 

 metamorphosis. Since this study does not involve the stages in 

 which secondary sex characters are present, we are concerned only 

 with the primary ones, namely, the presence of male or female 

 sex cell. Only the latter are structurally recognizable in the 

 stages studied, and they give us the only definite clue to the sex 

 condition of the young larvae. 



Oocj^tes appear in practically all lamprey larvae; in normally 

 dioecious species oocytes appear only in about one-half of the 

 young, while in the other half only male cells appear. Whether 

 or not male germ cells occur in all lamprey larvae cannot now be 

 stated for reasons already presented. When a germ cell, however, 

 shows no tendency to transform into an oocyte, but continues 

 to divide and form cysts, it has been assumed that it is poten- 

 tially more strongly male than female in constitution. The activ- 

 ity of the germ cells may be along either of two lines. In the 

 one case their tendency is toward growth, and in the other toward 

 rapid multiplication.. This difference in the activity of the cells 

 may be due to an inherent tendency in the cells themselves or to 

 factors operating in the cell environment. If due to the former 

 it must be admitted that all the germ cells of the same gland do 

 not have the same make-up and that during the process of devel- 

 opment each cell inherits a different constitution after each divi- 

 sion. Some of the cells are endowed with a tendency toward 

 rapid division and others toward an early cessation of division and 

 entrance upon a period of growth. It may be due to an unequal 



