The Sexual Phases of Myzostoma. 
251 
There is a remote possibility that the species here 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 Metacrmus moseleyi recorded among the hosts of the 
species described by v. Graff. 
9. M. pulvinar^ v. Graff. 
V. Graff (84 a, 84 b, pag. 41—42) first described this remarkable 
species from a single specimen »found upon the peristome of Antedon 
phalangimn Müll., 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. 2 1 ) shows that the specimen was distorted. This distortion 
is 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- 
vmar — Organs which v. Graff failed to discover — he has shown 
that the animal does not live upon the peristome of A. phalangium^ 
but that it is entoparasitic k He says {'92, pag. 847) : »il habite le tube 
digestif de son hote, dans lequel il est enfonce assez profondement 
pour etre invisible de Fexterieur. Le Myzostome occupe la presque 
totalite de la premiere partie du tube digestif de la comatule (oeso- 
phage et sac stomacal) et est situe de teile sorte que son extremite 
anterieure est tournee vers le pole aboral. Il s’appuie par sa face 
ventrale, fortement convexe et portant les dix parapodes, sur Fepi- 
thelium digestif de la comatule, tandis que sa face dorsale concave, 
regardant Forifice buccal de cette derniere, forme une gouttiere qui 
donne passage aux courants alimentaires, courants qui nourissent a 
la fois Fhote et son parasite. La disposition en gouttiere de la face 
dorsale du Myzostoma pulvinar explique comment celui-ci, malgre 
' Beard ('94, p. 403) speaks of this as »one of the eucysted species«. This 
is an instance of the care with which he has read Prouho’s paper and niy 
own preliminary note ('94, p. 181). 
