STUDIES ON THE ECTOPAKASITIC TEEMATODES OF JAPAN. 93 



The form and character of the penis are characteristic of the 

 genera, and will therefore be treated separately for each. 



(Diclidophora — In this genus the penis is an ellipsoidal body 

 situated right at the end of the vas deferens and bored by it through 

 the centre. It bears a certain number (the number varies in dif- 

 ferent species) of chitinous hooks, together constituting the chitinous 

 penis (PI. X, figs. 2 & 3; PJ. XI, fig. 4). The substance of the 

 penis consists of prismatic fibres arranged at right angles to its 

 central cavity, i.e., the vas deferens. These fibres are exactly like 

 those which have been described in the suckers of Microcotijle and 

 some other genera, both in their general .appearance and in their 

 reaction towards stains, and are separated from the surrounding mes- 

 enchyma by a distinct, structureless membrane. The chitinous hooks 

 are arranged at regular intervals on the external face of the penis 

 around the opening of the vas deferens, and although the proportions 

 of the dififerent parts vai-y in different species, they are constituted 

 alike in all the species of the genus described in this paper. Each 

 hook may be regarded as consisting of two portions, the basal and the 

 distal. The distal portion consists of a slender, chitinous thread, and 

 may be described as forming a loop, the free ends of ^vhich have fused 

 together (PL X, figs. 7 & 10). This sits by the round end of the 

 loop on the basal portion in such a way as to form an angle with 

 it. The basal portion is hour-glass shaped when looked at from the 

 front and is imbedded in the superficial part of the substance of 

 the penis-bulb by its triangular end (PJ. X, figs. 7 & 10, b). In 

 profile the basal portion looks somewhat triangular (PJ. XI, fig. 4). 



Octocotyle — In this genus the connective-tissue penis consists of 

 a median saucer-shaped body with two lateral bean-shaped bodies 

 mounted on its edge (PI. IX, figs. 5, 12, & 13). The median 

 body is pei'forated through its centre by the vas deferens, and 



