DICYEMIDS. 
473 
Group of Uncertain Position. 
To complete our account of the worms, mention must be made of the parasitic 
families Orthonectidce and Dicyemidce, of which the serial position is uncertain. 
tufted planaeian, Thysanozoum (enlarged twice). 
B 
Rhopalura. A, Male; B, Female. 
(Very much enlarged.) 
The members of the former inhabit 
the body-cavity of certain turbellarian 
and nemertine worms and brittle-stars. 
They are minute, segmented creatures, scarcely exceeding the twentieth of an inch 
in length, and without digestive organs or nervous system, but with the skin 
ciliated. The males are smaller than the females, being in the figured Rhopalura 
only about half the size of the latter. The Dicyemidce are ciliated, thread-like 
parasites, varying in length from about a thirteenth to a fifth of an inch in length, 
A dicyemid (enlarged 20 times). 
and living in the kidneys of cuttle-fish. The body consists of a central portion, 
composed of a single long, fusiform cell, around which is arranged a series of whiter 
cells, partly projecting like papillse from the surface. At the front end the cells of 
the external layer form a symmetrical head, by which the parasite attaches itself; 
but there are no distinct nervous, digestive, or muscular organs. 
R. I. POCOCK 
