STUDIES OX THE ECTOPARASITIC TREMATODES OF JAPAN. 43 



to accord with their supposed function. A prion', the opening 

 might be expected <jn the ventrul surface of the sucker ; hut 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 Hcxacotyle and Onclwcotijk 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 '^/o) solution 

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

 are very réfringent. When they are very slender they are wholly 

 solid ; but when somewhat large they are usually IkjIIow. 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. Tlieir 

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

 characteristic oï each species. 



In Oncliocûtijle, Tristomum, Monocotijlc, Calicot[iIc and Octocotijle 

 major 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 rouglily the 

 form of a fishing hook, and have a process at a]3out the middle of 

 their 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 posteriorly, but is turned mi^re 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 (PI. IX, fig. 2) ; but in Octoc. minor they are entirely 

 solid (fig. 9 a). 



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

 portion of the present paper. 



