A. L. COLWIN AND L. H. COLVVIN 139 



Response of Spermatozoon to Certain Stimuli 



Although there have been numerous studies on the morpho- 

 logical changes which the individual egg undergoes during fertili- 

 zation or parthenogenetic activation, there have been few inves- 

 tigations of the also important moiphological changes which the 

 individual spermatozoon undergoes at the critical time when it 

 becomes associated with the egg, or under conditions which may 

 be supposed to obtain at such a time. Yet theories of fertiliza- 

 tion must be in accord with the morphological features observed 

 during sperm-egg association and sperm penetration into the 

 egg. Most of the early studies were based chiefly on fixed 

 material. A few are of particular interest. Kupelweiser ( 1909 ) 

 and Meves (1915) studied fixed material of the mollusc Mytilus 

 edulis; both noted the complete disappearance of the "perfora- 

 torium" by the time the spermatozoon had entered the egg, and 

 Meves further noted that the perforatorium had disappeared even 

 from spermatozoa in process of entering the egg. Lillie (1912b) 

 pointed out that in Nereis the perforatorium of the fixed sperma- 

 tozoon is a rather straight filament, but he called attention to the 

 fact that in the living speniiatozoon the perforatorium is shaped 

 more like "the spike of a helmet" and is shoHer. 



Popa (1927) studied Arbacia spermatozoa suspended in egg 

 water with the expectation that any changes observed would 

 resemble those preliminary to fertilization. He reported that the 

 treatment caused the appearance of a small granule of sticky 

 substance which he thought was eliminated through the pointed 

 apex of the spermatozoon. Other changes in spenn morphology 

 also were noted. While Popa's observations are difficult to assess, 

 his experiments were at least an attempt at observation of the 

 individual living spermatozoon. 



Dan (1952, 1954; Dan and Wada, 1955) first demonstrated 

 clearly that on suitable stimulation the spermatozoa of a number 

 of species can undergo rather consistent profound morphological 

 changes. These changes aff^ect the acrosomal region and, to some 

 extent, the middle piece and flagellum. This reaction was termed 



