320 EDWIN E. REINKE. 



perforator! um and the very long tail-piece of the spermatozoa 

 found in forms like Littorina and Fasciolaria (Fig. 3). The 

 apyrene spermatozoa, on the other hand, bear very little re- 

 semblance to those described in other forms and to the eupyrene 

 spermatozoa they bear absolutely none at all. They are vrry 

 much larger than the latter and are outnumbered by them, 

 according to Brock's estimate, about I to 500; the correct numer- 

 ical relation existing between them in S. bituberculatus has not 

 been ascertained but it is probably the same as in S. lentiginosiis. 

 In length the apyrene spermatozoa average somewhat over 90 

 micra. 



The adult apyrene spermatozoon is composed of a central 

 spindle-shaped cell body, which is long and narrow and slightly 

 flattened dorso-ventrally, and two undulating membranes which 

 pass down either side of the cell-body (Fig. 2). At the anterior 

 end of the spermatozoon the membranes round out sharply to 

 their maximum width while posteriorly they narrow more 

 gradually and finally end in a short sharply pointed tail-piece. 

 The interior of the cell-body is filled with a number of large poly- 

 gonal bodies composed of an albumen, probably a nutritive 

 material. These bodies are more or less regular in shape and 

 position but they decrease in size at either end of the cell. 



The living spermatozoa, as they leave the sperm-ducts, do 

 not show any violent movements; at first long slow contraction 

 waves pass alternately down the two membranes in a postero- 

 anterior direction, propelling the spermatozoon in the opposite 

 direction, that is, the posterior end is directed forward. 1 Occa- 

 sionally a spermatozoon is seen moving with its anterior end 

 directed forward. The movement of the spermatozoon is com- 



1 In Paludina that end of the spermatozoon which contains the remains of the 

 nucleus, i. e., the head, has been designated as the anterior end and this is the end 

 which is directed forward in movement; it is also the end toward which the axial 

 fibers have grown. In Strombus, on the other hand, there is no nuclear head in the 

 spermatozoon and therefore, following the precedent established above, I have 

 designated as anterior that end toward which the axial fibers have grown. It 

 happens as a rule that in movement this end is dinvtrd backward. It was thought 

 better to orient the spermatozoon morphologically rather than by the direction of 

 movement. To be correct, the orientation should be reversed in both cases as the 

 end of the eupyrene spermatozoon toward which the axial fiber has grown is the 

 posterior one. 



