128 



STAEFISH GALLEEY. 



as ninety denticles. Trochetia suhviridis (Land-Leech) (96) is a 

 species which is found rarely and sporadically in England. 



TheMyzostomata(128, 129) form a division of Polychseta, all the 

 members of which live parasitically on Crinoids, and otherwise present 

 great differences in their habits. Some move about freely on the 

 Crinoids they infest, others are more sluggish and rarely move, 

 others produce galls or cysts on their host, and yet others are internal 

 parasites, and live in the alimentary canal. It is of interest to 

 note that there are corresponding degrees of difference between the 

 young and old specimens of the different groups of species. 



The general organisation of Myzostomata is shown in the 

 accompanying figure (Fig. 23) in which the dorsal wall of the body 



Fig. 23. 



Diagram of Myzostomum to show the general form of the body and the marginal 

 extensile cirri (c) ; "within these and on the ventral surface are four pairs of 

 suckers, and more iuteinally five pairs of appendages each bearing two 

 hooks ; the proboscis (p), the digestive tract and its ramifications, and the 

 reproductive organs are outlined as if seen through a transparent wall ; 

 a, anus. 



is supposed to be transparent so as to allow of the chief internal 

 organs being seen. 



