The Sexual Phases of Myzostoma. 
243 
given above: M. glahrum is dioecious from the time its reprodiictive 
Organs first api)ear, and like M. cirriferum it is functionally male 
in early life, then functionally hermaphrodite and finally function- 
ally female in its senile stages. The correlation of the migration to 
the disc of the Antedon and the development of functional herma- 
phroditism is not by any means perfect, since it is possible to find 
functional male individuals on the disc of the Aìitedon^ and inci- 
piently hermaphrodite individuals stili attached to the back and sides 
of the older Myzostomes. But in general it may be said that the 
change from the functional male to the functional hermaphrodite oc- 
curs when the animai shifts its positìon to the disc. 
4. M. alatum^ v. Graff. 
In form and habits this species closely resembles M. glahrum. 
My observations were made on half a dozen specimens obtained from 
the discs of a few Antedon phalangiiim^ Müller. The young are fonnd 
attached to the anterior dorsal surface of the older individuals. The 
ovary and testes are almost exactly like those of M. glahrum^ so that 
I may dispense wnth a special description and figures. The young 
individuals are functionally male, the larger ones functionally herma- 
phrodite. I bave not seen any functionally female specimens, but doubt 
not that they occur. 
Prouho's observations ('92) on this species, though incomplete 
in some particulars, v^ere evidently made on more material than I 
bave been able to secure, and as they offer very valuable support 
to my Interpretation of the sexual phases of the Myzostomidae, I 
may quote them bere. 
He says: »0n trouve, en effet, très fréquemment, sur le dos du 
M. alatum^ de soi-disant màles complémentaires, au nombre de un 
ou deux, rappelant exactement ceux qui ont été décrits par M. Beard 
chez le Myzostoma glahrum et que M. v. Graff avait eu probable- 
ment raison de considérer comme des jeunes. Or une sèrie d'obser- 
vations m'a montré, sans aucun doute possible, que les individus 
fixes sur les dos du Myzostoma alatum hermaphrodite sont de 
petits Myzostomes de son espéce qui, màles dans leur jeune àge, 
avec spermatozoides bien développés et conduits déférents pareils à 
ceux de l'adulte, grandissent et acquiérent, en grossissant, 
des ovaires identiques à ceux de l'hermaphrodite qui les 
Supporte, et cela sans abandonner les dos de ce dernier.« 
Mittheilungen a. d. Zoolog. Station zu Neapel. Bd. 12. 17 
