THE ANNULUS OF A MEXICAN CRAYFISH. 



131 



In both cases the first loop of the suture showed the thin plate 

 of wax-like material represented in Fig. 10 as the darkened mass 

 along the first curve of the suture. This wax also projected on 

 the lateral face as the "sperm plug" so much more conspicuous 

 in C. ajftnis. Now the oozing out of such a film of wax and the 

 extension of the sperm from the suture over the annulus is what 



Fig. 10. 



was made out, with difficulty, in the specialized annulus of C. 

 affinis when mechanical pressure was exerted upon the annulus 

 by forcing the hard sternum of the last thoracic somite against 

 the annulus. 



In these C. montezumcz the sperm may have been forced out 

 of the pocket by the shrinkage due to the heat with which they 

 were probably killed, or the issuance of sperm may have been a 

 normally produced act in females about to lay and in that case 

 the efficiency of the spine upon the sternum of the fifth legs 

 (Fig. 1) as a means of squeezing the annulus against the sterna 

 in front of it, seems to support the view that it is such spon- 

 taneous pressure on the part of the female that liberates the sperm 

 at the right time to meet the eggs. 



