WORMS. 
125 
as ninety denticles. Trochetia sulviridis (Land-Leech) is a species 
which is found rarely and sporadically in England. 
The Myzostomaria form a division of Polychaeta 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 Myzostomaria is shown in the 
accompanying figure (Fig. 23) in which the dorsal wall of theHbody 
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 internally 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. 
