NO. 1791. 



SPERM I'RANSFER TN DECAPODS— ANDREWS. 



427 



substance of the shelf while its posterior horns diverge widely and 

 branch in the substance of the scale plate. The middle of the 

 H -shaped cavity is also somewhat prolonged posteriorly between the 

 beginnings of the posterior horns. 



No specunens were found with sperm in the thelycum, but its 

 structure seems well adapted to hold sperm masses. 



The above fragmentary observations suffice to show that in some 

 of these prawns, the Peneidie, the thelycum is used as a spermatheca 

 and that it is morphologically a space inclosed more or less by out- 

 growths from the shell. 



Turning now to another group of Decapods, the Eryonidea, in 

 which a spermatheca is said to occur, we find in specimens in the 

 collections of the U. S. National Museum no sign of a spermatheca, 







. r--.-,. 7 ■.■ fci; 





Fig. 10.— Section across the middle of the thelycum, posterior to the sections shown in 

 Figs. 8 and 9, with the shelf (S) overarched by the scales (Sc). 



but, however, a well marked spermatophore mass applied to the sur- 

 face of the sternum of the female in the region of the thelycum of the 

 Peneidse. 



In Polycheles granulatus the sternum of the female is composed of 

 three well-marked plates in the region to be studied, one between 

 the fourth legs, one between the fifth, and a third somewhat pos- 

 terior to the fifth legs. Laterally these plates are marked off from 

 one another by grooves, but along the median region they form one 

 continuous shell that is depressed so that the anterior part rises up 

 markedly above the posterior part. There is no indication of any 

 elevated ridges or plates at all comparable to the thelycum and no 

 holes or cavities that could function as a sperm receptacle. The 

 same general structure and absence of any receptacle was seen in 

 specimens labeled Willemoesiainornata, Eryoneicus indicusliawaiiensis, 

 and Eryoneicus csecus. 



In the young or smaller specimens of Polycheles sulimi and P. 

 sculptus the same is true, but in older or larger specimens there are 



