MtsceUa neous. 71 



aliraontar)' canal of its host, in which it is sufficiently deeply 

 ensconced to be invisible from the exterior. The Mifzmtoma occupies 

 almost the whole of the first portion (oesophajius and stomachal sac) 

 of the alimentary canal of the Comuiula, and is situated in such a 

 •way that its anterior extremity is turned towards the aboral pole. 

 It applies itself by its ventral face, which is very convex and bears 

 the ten parapodia, to the digestive epithelium of the Comatida, wliile 

 its concave dorsal surface, looking towards the buccal orifice of the 

 latter, forms a channel which affords a passage to the food-currents, 

 which nourish at once host and parasite. The gutter-like form of 

 the dorsal surface of Mi/zostorna pulvimti' ex\Aii\ns how it is that the 

 latter, in spite of its considerable dimensions, does not completely 

 obstruct the alimentary canal of the Comatnla. 



Mijzostoma pulvtanr, which is the first endoparasitic form 

 belonging to this genus with which we are acquainted, is a dioecious 

 species with well accentuated sexual dimorphism. In this, as in 

 other points of its organization, it approaches the cysticolous 

 members of the genus. 



In linear dimensions the female is four and a half times larger 

 than the male ; it measures 4-5 millim. in each direction. It 

 presents no trace of testes either in the adult or young state. As in 

 the hermaphrodite species, its uterus communicates with the exte- 

 rior by three ducts — a median one, which is a direct prolongation 

 of the uterus itself, and two lateral ones, which open into the ante- 

 rior portion of the cloaca (rectum). 



The male only measures 1 millim. in length by 0*8 millim, in 

 breadth ; it hooks itself on to the integument of the female, upon 

 which it is able to move pretty rapidly. In shape it is flattened 

 and elliptical, recalling by the form of its body the free species of 

 ]\Ji/zostoiiia. Its alimentary canal is not branched, but exhibits on 

 each side indications of the three ramifications which are seen in all 

 the other species of the genus ; its mouth, which is situated quite 

 close to the marginal border, is ventral in position. It possesses 

 two testes, one on each side of the alimentary canal, and each pro- 

 vided with a vas deferens which opens on the vential surface. 



The two sexes must become associated at a very early period, for 

 I have observed a young female measuring 1-7 millim. in length 

 which bore upon its back a male of 0-7 millim. The female in this 

 instance did not as yet present any trace of ovaries, but already had 

 the characteristic form of the adult. 



M ijzostovia alatum. — This species lives as a parasite upon the disk 

 of Anteclon phalanjium^ and its relations to its host are the same as 

 those of Myzoxtoma fjlahrum to Antedon rosacea : its anatomy does not 

 essentially differ from that of Mijzostoma glahrum. Like the latter 

 it is hermaphrodite, and my object in drawing attention to this 

 species is occasioned by the fact that the observations which I have 

 been able to make with regard to it raise a serious doubt as to the 

 existence of the so-called comidemeutal males in the hermaphrodite 

 epecies. It is true that there are very frequently found upon the 



