A. L. COLWIN AND L. H. COLWIN 



147 



more effective stimulant. Thus as shown in experiment 7 of 

 Table I, with samples from the same original sperm suspension 

 egg water was ineffective whereas alkaline sea water caused at 

 least 92% of the spermatozoa to produce acrosome filaments. 

 Since untreated (control) sperm suspensions sometimes show a 

 very low percentage of spermatozoa with acrosome filaments, it 



Oj 



9r 







L. 



zo 



MO 



A 



Fig. 26. Reacted spermatozoa showing acrosome filament, from photo- 

 graphs of living specimens. (From Colwin and Colwin, Biol. Bull., 1956.) 

 a— c, Thyone biiareus; d-e, Asterias forbesii. a, in egg water (35 microns); 

 b, at egg surface (48 microns); c, in alkaline sea water (75 microns) (po- 

 sition of distal part of flagellum modified for reasons of space); d, in insem- 

 inated culture but directed away from egg (15 microns); e, at egg surface 

 (22 microns). 



would seem possible that other factors, as yet unknown, may also 

 evoke the acrosome reaction. 



The changes which the spermatozoa undergo when suitably 

 stimulated are seen readily in living preparations. Figure 28 

 shows an unreacted spermatozoon for comparison with others 

 which have reacted to treatment with alkaline sea water (Figs. 

 26c, 29 and 30) or with egg water (Figs. 26a and 31). Reacted 

 spermatozoa may be found also in preparations of inseminated 

 eggs. The sperm head is connected with the egg surface by a 



