SANGUINICOLA 241 



of shells, it seems to be evident that the eggs must be removed 

 from the blood by the agency of some such external blood- 

 sucking parasite as (in the case of the German Sanguinicola 

 of the carp) the carp-louse, Argulus folia ceus, or (in 

 the case of the Sudan Sanguinicola) other species of Argulidae, 

 or perhaps a leech. In Odhner's sketch of the possible life- 

 history of the German Sanguinicola he omitted to offer any 

 suggestion as to how the fertilized eggs reached the MoUuscan 

 intermediate host postulated by him from the fish, other than 

 stating that he found a ' mature ' egg, containing a miracidium, 

 in the kidney of a carp, but to me it is difficult to believe, without 

 further evidence, that a miracidium can develop from a shell- 

 less egg in blood and thence take to water. All animals (except 

 perhaps sponges and other very low forms of aquatic life) 

 which extrude eggs into water, even when the animals them- 

 selves are living in water, and even when the eggs are not 

 fertihzed until after contact with the water, protect the eggs 

 with shells or envelopes of one kind or another, and much more 

 should this be the case in parasitic forms (hke Schistosoma) 

 which have to extrude the eggs first into vertebrate blood and 

 then into open water. 



As regards the external vaginal groove, this is possibly 

 connected with the insertion of the penis, though it is difficult 

 to understand on that hypothesis why its direction should be 

 at right angles to that of the vagina and not in line with it. 



Finally, I must state that I have adopted the convention of 

 regarding the surface of the body bearing the longitudinal 

 furrow as the dorsal side, because it is usual in both Turbellaria 

 and Trematoda for the sexual openings to be situated ventrally. 

 The fact that in certain Trematodes a similar furrow is situated 

 on the ventral side is but of little importance in this connexion 

 because it is probable that the furrow in Sanguinicola is a special 

 structure adapted to life in blood-vessels, and I am by no means 

 convinced, in view of the Turbellarian conformation of the 

 genitalia in Sanguinicola, that Odhner is right in regarding 

 Sanguinicola as a Malacocotylean, despite the analogies (of the 

 gut and habitat) with Aporocotyle and Deontacylix, though it 

 is true that the genitalia of Sanguinicola may have become 



