EEPOET ON THE MYZOSTOMIDA. 
21 
It appears from the two foregoing lists that the sixty-eight species of Myzostomida 
are distributed upon fifty-two hosts in the following manner : — 
48 species have each 1 host. 
13 „ „ „ 2 hosts. 
6 ^ ^ 3 hosts. 
1 ,, „ „ 4 hosts. 
In those cases, however where one species infests more than one host, the latter are 
always closely allied, and in no case is there an instance of a single species of this parasite 
being found both upon a stalked Crinoid and one that has no stalk. 
With regard to the number of different species of Myzostomida that are found upon 
a single host it appears that 
31 species of Crinoidea are infested 
12 
77 77 77 
77 
77 
77 
5 ) 
hy 1 species of Myzostoma. 
77 
77 
77 
77 
77 
Systematic Remarks. 
The definition of the group Myzostomida, which I place as an Order in the Class 
Stelechopoda (Genus Myzostoma, p. 71), must be altered to admit the new form 
Stelechopus hyocrini (see special description) ; this species has a straight alimentary 
canal and no suckers nor male genital apertures. There are also other forms that are 
more certainly dioecious. 
Order Myzostomida. — Symmetrical non-segmented animals, provided with an ex- 
ternal chitinous cuticle, five pairs of movable parapodia, each with a hook and 
supporting rod, an alimentary canal with oral and anal apertures ; through 
which latter the eggs are extruded. Dioecious or hermaphrodite; central 
nervous system consisting of an oblong mass situated beneath the intestine, 
and giving off two branches in front which encircle the pharynx, but bear no 
ganglia, and several other pairs of lateral nerves. No circulatory, respiratory, 
nor excretory organs. Parasitic on and in Crinoids. 
Family I. Stelechopidce . — Myzostomida with straight alimentary canal ; parapodia 
independent of each other ; no internal muscular septa. Suckers absent. Pro- 
bably hermaphrodite, sexual products reaching the exterior through a cloaca. 
Family II. Myzostomidce . — Myzostomida with ramified alimentary canal, parapodia 
connected by muscles which converge to a central muscular mass. Body 
