98 S. GOTO. 



but the mesenchyma around the terminal portion of the vas deferens 

 has assumed a character more or less different from that of the other 

 parts ; and although it is not so distinctly separated from the remaining 

 portion as in Onchocotyh, it still forms doubtless the morphological 

 equivalent of the penis. Physiologically, too,, this portion seems to 

 deserve the name, since in Hexacotyle (PI. XII, tig. 6) numerous 

 muscular fibres take rise from the papilla on the top of which the vas 

 deferens opens, and taking mostly a direction backwards are inserted 

 into the dorsal wall of the body. These constitute doubtless the 

 retractor muscle. In Azine (PI. VII, fig. 5 ; PI. YIII, fig. 3) I have 

 not been able to demonstrate the presence of any retractor ; but the ter- 

 minal portion of the vas deferens is surrounded by a mass of connective 

 tissue which is very similar to that of the penis of Onchocotijle with the 

 only difference that the meshes are closer and the fibres finer, and 

 which remains wholly unstained by borax-carmin. An exactly similar 

 tissue is present in Microcotyh reticulata (PI. Y, fig. 6), a species 

 which approaches in many respects the genus Axine. Had a mem- 

 brane been developed around this peculiar mass of connective tissue 

 nobody would hesitate to call it the penis; but as it is, we am not 

 give it a distinct boundary. Physiologically, however, there is little 

 doubt that this tissue acts as a true penis; for in Microcotijle reticulata 

 and Axine aberrans the internal surface of this part of the vas deferens 

 is armed with numerous chitinous spines (PI. V, fig. 6 ; PI. VII, 

 fig. 6 a). In the former species each spine consists of a hemispherical, 

 basal portion and a spinous, distal portion, and is perfectly straight ; 

 in the latter species the spines are simple and are slightly curved. It 

 is difficult to conceive the use of these spines unless the portion that 

 bears them can be evaginated. 



The chitinous copulatory organ of Microcotyle is somewhat dif- 

 ferent from those hitherto described, and will be tre.ated of in connec- 



