STUDIES OX THE ECTOPAKASlTIC TKEMATODES OF JAPAX. IQJ 



name that portion of the female efferent duct that lies betweea the 

 ovary and the ootyp, the beginning of the latter being always distinctly 

 marked by numerous unicellular shell-glands. Its course and its 

 relation to other genital ducts are very different in different species, 

 and vnW be described afterwards for each species in the systematic 

 part, but some of its common features must be noted doAvn here. It 

 lies, namely, in all the species dorsal to the unpaired yolk-duct, and 

 communicates with it as well as with the canalis gcnito-intestiiudis when 

 such is present. In Mtcrocotijle, Axinc, Onclwcotijlc. Dididophora, and 

 Calicoti/le it bears the receptaculum seminis. In the first two genera 

 just mentioned this organ is formed simply either by a lateral evagiua- 

 tion, or by the swelling of a portion, of the oviduct ; and seems to be 

 actually present only when it is filled mth sperm mass, and to 

 shrink together when there is no sperm to fill it. so that then it 

 seems as if entirely wanting. In Dididophora the receptacidum 

 seminis is exceedingly large, and is very conspicuous, es^Decially in 

 Didid. sessilis (PI. X. fig. 5). In this species it is a very large 

 sac situated on the median line of the body just behind the ovary, 

 and consists of numerous lobes. These lobes are mostly situated 

 on the dorsal side of the lx)dy, and are separated from each other 

 by a thin layer of connective tissue. They all convei'ge towai-ds the 

 oviduct as a centre, and communicate with it just where it makes 

 a short forward bend to meet the unpaired yolk-duct (PI. X. fig. 5 ; 

 PI. XI, fig. 5). In cross-section the cavities of the lobes are seen to 

 be destitute of any distinct lining membrane. In all the specimens 

 I have examined, they were always completely filled with sperm-mass. 

 In Didid. dongata the seminal receptacle is also large, but is consider- 

 ably smaller than in Didid. sessilis^ and is simply globular in shape 

 (PL X, fig. 9). In Didid. tetrodonis I have not observed any seminal 

 receptacle, but this was, I believe, owing to the absence of any sperm 



