82 W. W. SWINGLE. 



PLATE II. 



FIGS. 7, 8 and 9. Spermatogonia of Rana pipiens, showing twenty-five chro- 

 mosomes. 



FIGS. 10, ii, 12 and 13. Spermatocytes, showing prophases of the first matura- 

 tion division. 



