DICYEMIDS. 

 GROUP OF UNCERTAIN POSITION. 



473 



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. 



Rhopalura. A, Male; B, Female. 

 (Very much enlarged.) 



The members of the former inhabit 



TUFTED PLANARIAN, Thysanozown (enlarged twice). 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 DICTEMID (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 papilla 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. 



E. I. POCOCK. 



