231 
At no stage observed were there transitional forms between ve- 
getative cells and spermatogonia. It appears quite certain that many 
spermatogonia are left in the walls of the seminiferous tubules after 
the September period of sperm formation. Those observed in the 
specimen killed October 20th, were exactly like those seen in the 
turtle killed on September 10th. For several months there is now no 
sexual activity, until upon the approach of spring, when the sperma- 
Fig. 15. Fig.814. 
Fig. 12. Portion of a seminiferous tubule of an adult killed Sept. 10th. X 721. 
Near the periphery of the tubule to the left, is seen a Sertolian cell, to the right of 
which are two spermatogonia. Above, are a number of spermatids and spermatozoa. 
Fig. 13. Portion of a seminiferous tubule of an adult killed Oct. 20th. X 721. 
Three spermatogonia of different size are shown near the periphery of the tubule, while 
three nuclei of Sertolian cells occur nearer to the lumen. 
Fig. 14. Portion of a seminiferous tubule of an adult killed on Jan. Ist. X 721. 
Near the periphery, are seen four spermatogonia and two Sertolian cells, while nearer 
the lumen there appear seven spermatocytes in pre-synapsis and synapsis stages. A de- 
generating sex-cell is seen at the left. 
Fig. 15. Two spermatogonia and a Sertolian cell found in the same section as 
Fig. 14. X 721. This shows one of the largest and one of the smallest spermatogonia 
to be found at this stage. 
togonia are found to be multiplying and transforming into spermato- 
cytes. Several other stages intermediate between those mentioned, 
