STUDIES OX THE ECTOPAEASITIC TREMATODES OF JAPAN. 43 



to accoi'd with their supposed function. A priori, the opening 

 might be expected on the ventral surface of the sucker ; but as the 

 matter stands, I suppose the secretion of the glands flows over the 

 dorsal surface of the sucker on to its margin, and here helps to attach 

 it more firmly to the host. 



The two genera Hexaeotyle and Onchocotyle are destitute of any 

 sticky gland. 



Hooks'' — These are usually spoken of as of a chitinous nature ; 

 but it should be remembered that they are soluble in a (35 "jg) solution 

 of caustic potash. In the natural state they are slightly yellow, and 

 are very refringent. When they are very slender they are wholly 

 solid ; but when somewhat large they are usually hollow. They lie 

 mostly imbedded in the mesenchyma, and only a very small portion 

 of the pointed end projects free on the surface of the body. Their 

 form, size, number, and position are very varied, but are emiiiently 

 characteristic of each species. 



In Onchocotyle, Tristomum, Monocotyle, Calicotyle and Octocotyle 

 Tiiajor there is only a single pair of hooks. In the last-mentioned 

 species, they are situated at the posterior end of the body between the 

 posterior suckers, close to the median line. They have roughly the 

 form of a fishing hook, and have a process at about the middle of 

 there length, to which is attached a strong bundle of muscular fibres 

 (PI. IX, figs. 2 & 9 a). In the natural position the pointed end is 

 usually directed postyCriorly, but is turned more or less in other 

 directions according to the different states of contraction of the muscle 

 attached to the hook. In Octoc. major the hooks are hollow towards 

 the pointed end (PL IX, fig. 2) ; but in Octoc. minor they are entirely 

 solid (fig. 9 a). 



1). For more minute descriptions of the hooks in different species see the systematic 

 portion of the present paper. 



