26 PHYSIOLOGICAL TRIGGERS 



in the absence of an adjuvant (57). Finally, these observations confuse the 

 picture for normal fertilization in the starfish. The formation of a filament 

 extending through the egg jelly from the sperm to the egg surface appears to 

 be a normal, and perhaps essential, initial step in starfish fertilization (14, 20, 

 28, 40). A comparable situation appears to obtain in the enteropneust, Sac- 

 coglossus, for Colwin and Colwin (18) in a very thorough study have described 

 and illustrated with photographs an acrosome filament extending from the 

 sperm head through the egg membranes to the egg surface in this form. Dan 

 (23) has suggested that the starfish filament is an acrosome filament formed in 

 response to egg products. However the data presented in table i indicate that 

 acrosome filament formation depends upon a metal-binding agent as well as 

 the egg water. The presence of such an agent under natural conditions seems 



Table i. Percentage of asterias forbesu and nereis limbata sperm with 

 acrosome filaments following treatment with egg water 



Nereis^ 85 (48) 30 (90) 



* Figures in parentheses are the numtjer of spermatozoa examined and recorded. Only 

 sperm with acrosome region lying free and unobstructed upon the collodion membrane were 

 recorded. This may have introduced a selective error in the data, especially in the case of 

 fertilizin treated sperm, for it eliminates most cells in clumps and agglutinates. The ag- 

 glutinates might be expected to contain a high percentage of sperm with filaments. 



t In two other experiments no filaments were observed on egg water treated or control 

 sperm. However, the egg water did not agglutinate the sperm in these two experiments 



unlikely. Certainly fresh, normal egg water lacks the necessary chelating action. 

 Possibly the acrosome reaction results from contact with the egg jelly (20). 



Three experiments were performed on Nereis sperm. In two of these, no 

 acrosome filaments appeared on either sea water or egg water treated sperm, 

 but in a third experiment filaments were found on both (table i). The egg water 

 agglutinated the sperm strongly in the last experiment. Treatment with egg 

 water appeared to effect a three-fold increase in the percentage of sperms with 

 filaments. Evidently Nereis sperms possess acrosome filaments under certain 

 conditions. These filaments may be formed in response to egg water under 

 agglutinating conditions. They may also be produced under other conditions, 

 perhaps as a result of contact with glass. It is of interest to note that the form 

 of the Nereis sperms with filaments as seen with the electron microscope closely 



