322 J- Beard 



certaiu, that, even if tlie male be associated with a hermaphrodite, 

 some of the eggs of the latter will be fertilised by the former, and, 

 thus, the further production of male forms rendered more certain. 



In other circumstances, more especially where the forms are 

 free, as in M. cirriferum^ the chances of a male meeting with a 

 hermaphrodite, upon which to settle, must be small. There can be 

 no close association of male and hermaphrodite bere. And, as a 

 matter of faet, it would be difficult, or impossible, to fix upon a 

 single freely moving species in the animai kingdom, in which there 

 is such a close association of male and f'emale, or of male and 

 hermaphrodite throughout life. 



The intimate association is out of question, and, thus, the fer- 

 tilisation of eggs by the male becomes rare, and, finally, perhaps 

 very soon, ceases. Then the males rapidly disappear. 



And now, to come back to Myzostoma^ »der lehrreichsten aller 

 Wurmgattungen«, as the late Feitz Müller sagely remarked! 

 Owing to the various kinds of parasitism presented by the numerous 

 species of the genus, parasitism, which in some cases has tended 

 to the preservation of the males, in others to their extinction, in yet 

 others to their conversion into hermaphrodites, we can, so far as at 

 present known, divide the species up into: — 



1 . Purely dioecious forms with small M. pulvinar and some 

 males. (von Graff, Prouho.) cysticolous species. 



2. Hermaphrodite forms with true males, M. glahrum. 

 which remain male. (Beard.) 



3. Hermaphrodite forms with males, M. alatum. 

 which, retaining their positions on 



the hermaphrodite, afterwards be- 

 come female. (Prouho.) 



4. Hermaphrodite forms, in which the M. cirriferum and 

 males bave lost their dorsicolous others. 

 Position, and have either become ex- 



tinct or converted into protandric 

 hermaphrodites. 



