The Sexual Pliases of Myzostoma. 
251 
There is a remote possibility that the species bere described 
from such poor specimens may belong to one of v. Graff's species. 
The young individuals of the cysticolous species differ so widely 
from the adults that it is impossible to refer it to any of the described 
species ; nor is Metacrinus moseleyi recorded among the hosts of the 
species described by v. Graff. 
9. M. pulvinar^ v. Graff. 
V. Graff (84 a, 84b, pag. 41—42) tìrst described this remarkable 
species from a single specimen »foiind upon the peristome of Antedon 
phalangium Mlill., dredged in the Minch from 60 — 80 fathoms, Aug. 14, 
1869 by H. M. S. ,Porcupine^(. The specimen was 2.7 mm long and 
3.2 mm broad. In the main v. Graff's description is correct, although 
one of the figures, representing the dorsal aspect of the Myzostome 
(PI. 3 Fig. 21) shows that the specimen was distorted. This distortion 
iß not perceptible from the ventral side (Fig. 22). v. Graff considered 
the species to be allied to M, radiatum — a relationship which I 
believe must now be considered very doubtful. 
A very considerable advance in our knowledge of the structure 
and habits of this species has been made by Prouho. Besides 
cailing attention to the existence of rudimental suckers in M. pul- 
vinar — organs which v. Graff failed to discover — he has shown 
that the animai does not live upon the peristome of A. phalangium^ 
but that it is entoparasitic ^. He says ('92, pag. 847) : »il habite le tube 
digestif de son hòte, dans lequel il est enfoncé assez profondément 
pour étre invisible de l'extérieur. Le Myzostome occupe la presque 
totalité de la première partie du tube digestif de la comatule (oeso- 
phage et sac stomacai) et est situé de teile sorte que son extrémité 
antérieure est tournée vers le pòle aboral. Il s'appuie par sa face 
ventrale, fortement convexe et portant les dix parapodes, sur Fépi- 
thélium digestif de la comatule, tandis que sa face dorsale concave, 
regardant Forifice buccal de cette derniére, forme une gouttière qui 
donne passage aux courants alimentaires, courants qui nourissent à 
la fois l'hòte et son parasite. La disposition en gouttière de la face 
dorsale du Myzostoma pulvinar explique comment celui-ci, malgré 
' Beard ('94, p. 403) speaks of this as »onie of the eneysted species«. This 
is an instance of the care with which he has read Prouho's paper and niy 
own preliminary note ('94, p. 181). 
