MIGRATION OF SEX-CELLS OF FUNDULUS HETEROCLITUS. 3^3 



influenced by the action of the swim bladder. One of these lost 

 cells is shown in the mesentery in Text Fig. D. The future of 

 such cells is an open question. 



A count of the sex-cells in this embryo, B 42, gave 64. There 

 was never any question of recognizing these cells, for no cells of 

 doubtful character were observed. Four of these cells found 

 were in the mesentery above the gut, and one was in the loose 

 tissue ventral to the Wolffian duct. No cases of disintegrating 

 sex-cells were observed in our Fnndnlus material, although such 

 conditions are reported by some investigators. 



The 2^-day embryo shows the next advance in the germinal 

 path. This stage has been considered perviously in connection 

 with " Criteria of the Primary Sex-Cells." 



TABLE OF AVERAGE DIAMETERS. 



For the purposes of this investigation the diameters in micra 

 were found by averaging the long and short dimensions of the 

 cell and nucleus. By this method a number of representative sex- 

 cells of embryos in all stages of migration were measured under 

 the oil immersion and the following results were obtained. 



Multiplication of tlic Sc.v-cclls. 



The early distribution of the sex-cells (Figs. 20 and 21) is best 

 explained, we believe, in connection with the streaming of the 

 organ-forming substances which contribute materials to the em- 

 bryo body. In most processes of this nature not only cell trans- 



