658 



D. B. CASTEEL 



the substance which forms the walls of the proximal half of the 

 outer tube is drawn into the basal region of the inner tube. 

 From the very beginning of its formation the inner tube con- 

 tains mitochondria, and as its growth progresses it draws into 

 itself all of the mitochondria of the cell (figs. 27, 28, 29, and 30) . 



Text fig. 1 Outline drawings of illustrative stages in the formation of the 

 spermatozoon, showing its relative form and size at different periods of develop- 

 ment. All stages here represented are from camera lucida drawings of living 

 material at the same magnification. The numbers refer to approximately similar 

 stages shown in the plates. 



