547 



eine gegenseitige Stellung, die für die Übertragung der Spermas auf 

 die weiblichen Teile nur von Vorteil sein kann.« 



Ortmann also states tliat female organs analogous to the Thelycum 

 are entirely unknown in all other groups of the Decapoda. 



Since that date, however, it has been shown that in the crayfish of 

 the genus Camharus ^ there is a female organ used in conjugation which 

 has the same location upon the thorax as the Thelycum. 



This fact, together with the striking parallelism between the Fe- 

 tasma on the one hand and the first male abdominal limbs of the cray- 

 fish on the other, in that both are of characteristic form in each species, 

 led me to infer that since the male limbs of these crayfish were found 

 to transfer sperm into the sperm receptacle of the female that the ex- 

 ceptionally modified limbs of the males in the Penaeidea might be used 

 to transfer sperm into some receptacle to be sought for in the Thelycum. 



An examination of the Petasma in some specimens of Pm^apenaeus 

 constrictus shows that it is well fitted to transfer sperm from the open- 

 ings of the defferent ducts through the length of the organ to its anchor 

 shaped tip and thence out through a groove in each arm of the anchor 

 to the special termination right and left. The Thelycum in this species 

 prooves to be a well protected pocket, right and left, with complex an- 

 terior and posterior horns and by applying the male to the female it 

 seems probable that the tips of the Petasma might be made to discharge 

 sperm right and left into the two lateral pockets that lie concealed 

 within the Thelycum. 



A subsequent anatomical study of the Petasma in Penaeus brasilien- 

 sis shows that it also might function as an organ to transfer sperm from 

 the openings of the defferent ducts to the Thelycum. The Thelycum in 

 this species, though outwardly very much like that in the above species 

 of Parapenaeus contains a remarkable chitinous bag, with exceedingly 

 narrow external opening and this bag contains large quantities of sperm 

 in several females. 



It is thus proven that the Thelycum may contain sperm and as the 

 Petasììia seems well fitted to put the sperm into the Thelycu7n we seem 

 to have an explanation of the use of these two organs. 



In confirmation of this view we note that Spence B ate in the above 

 Challenger paper, in describing specimens, all females, of Hemipenaeus 

 tomentosus figures and describes the Thelycum as a deep depression, but 

 in one case this is figured as filled up by a mass that projects all round 

 about the depression and is referred to in the explanation of plates 

 as a gelatinous mass, though in the text the author says ,,the deep 



1 Andrews, The annulus ventralis. Proc. Boston Acad. Nat. Hist. 32. 1906. 



35* 



