THE TREMATODA 



1858) has meanwhile changed. Gasterostomum, sp. of the shark, has 

 as first intermediate host Ostrea, Cardium, etc., whence issues Buceph. 

 haimeanus, which makes its way into a second host, the fish Belone. 

 The sporocysts castrate the mollusc which they attack. FAMILY 6. 

 DIDYMOZOONIDAE, Montic., live in pairs, encysted on the surface, oral 

 cavity, or branchial chamber of fishes; the anterior sucker alone is 

 present ; the genital pore is in front of the oral sucker. Didymozoon, 

 Taschb. (Fig. X. 6, 9) ; Nematobothrium, v. Ben. 



A 



B 



FIG. XIV. 



Bucephalus polymorphiis, v. Baer. The forked-tailed cercaria of Gasterostomum fimlmatum, 

 v. Sieb. The cercaria occurs in Anodon, etc., the adult in Leuciscus, sp. A, the body ; B, the 

 bifurcate tail ; a, the pharynx, behind which is the mouth, in the centre of the body ; b, the 

 pear-shaped glandular organ, which is replaced by the anterior sucker during its metamor- 

 phosis ; c, the ansatzstiick at the base of each limb of the bifurcate tail ; between them is seen 

 the base or median portion of the tail. 



Further Remarks on the Order Malacocotylea. Whereas the 

 general statement is true that sexual forms of this group occur 

 only in Yertebrata, there are at least two species of Distomum 

 which constitute exceptions : 



D. echiuri, Greef, is found in the nephridium of the male 

 gephyrean Ecliiurus pallasii. D. rhizophysae, Stud., occurs in 

 the siphonophorous hydrozoan, Ehizophysa conifera. An encysted 

 Distoma has been found in the tentacles of Synapta, and the 

 viscera of Ophiurids, by Cuenot (1892). 



Further, several sexless, not encysted, cercariae have been 

 recorded from various marine non-molluscan animals : D. pelagiae, 

 Koll., in the gonads of Pelagia ; D. hippopodii, C. Yogt ; D. cesti- 



