The Sexual Phases of Myzostoma. 
229 
this may be left to future investigators; for the purposes which 1 
have in view I propose to group the species according to their ha- 
bitSj thus: 
I. Migratory species; i. e. species wliicb move about freely on 
the Crinoids which they infest. Type: M. cirriferum^ Leuck. 
II. Stationary species; i. e. sluggish species which rarely if 
ever leave the spot where they have settled on the Crinoid. Type: 
M. glabrum^ Leuck. 
IIL Cyst-producing species; i. e. species which produce galls 
or swellings on the discs or arms of their Crinoid hosts. Type: M, 
cysücolum^ v. Graff. 
IV. Entoparasitic ‘species; i. e. species which inhabit the 
alimentary tract of their Crinoid hosts. Type : M. pulmnar^ v. Graff. 
All the species of these various groups may be arranged in a 
series of increasing parasitism, or, strictly speaking, commensalism, 
from the primitive and most typical forms of the first group to the 
very aberrant species of the fourth group. The departure in the 
adult from the juvenile condition increases in a corresponding manner: 
the young and adult of forms like M. cirriferum being very similar, 
while the young and adult of M. puhinar are very dissimilar. The 
nine species which I shall consider in the present paper may be 
distributed among the four groups as follows : 
I. Migratory species | 
II. Stationary species | 
III. Cysticolous species | 
IV. Entoparasitic species { 
M. cirriferum^ Leuck. 
M, circinatum^ n. sp. 
M. glabrum^ Leuck. 
M. alatum^ v. Graff. 
M. platypus^ v. Graff. 
M. heilig n. sp. 
M. cryptopodium^ n. sp. 
M. eremita^ n. sp. 
M. pulvmar^ v. Graff. 
1. Myzostoma cirriferum^ Leuckart. 
The habits and general structure of this commonest of the 
Mediterranean species of Myzostoma have been so fully described 
by Loven ('42), v. Graff ('77), Nansen ('85) and others, that I 
may here restrict my account to the reproductive Organs and the 
sexual phases. Düring February and March nearly all the specimens 
16 * 
