1918.J t. Southwell & B. Prashad : Parasites of HtUa. 81 



chohothrius ilisha occurs in the lateral muscles of Hilsa. This fish is 

 eaten by the shark Carcharinus yangeticiis, and practically all stages 

 between the cystic form and the adult worms are to be found in the 

 intestine of the shark in question. 



Three points arise for consideration : — 



(1) We have already called attention to the fact that the tail of the 

 tadpole-like cyst is mobile. It appeared to us on examining the living 

 material, in situ, that the movements of the tail were directed toward 

 retaining the cyst in the lumen of the shark's intestine, until the larva 

 had had time to emerge and attach itself to the wall of the gut. 



(2) We have no information as to the exact manner in which the Hilsa 

 become infected. The eggs of the adult worm are obviously shed 

 into the water. Most probably they are swallowed accidentally by the 

 Hilsa, in which case the larva would be liberated and carried to the 

 muscles, via the lymph or the blood stream. It is further possible that 

 the larvae hatch out in water, and, attaching themselves to the Hilsa, 

 bore their way to the lateral muscles ; but as we know nothing regarding 

 the structure of the larva, we can only hazard a guess as to the initial 

 mode of infection of the Hilsa. 



(3) It will be clear that parasites occurring in the intestines of fish 

 are removed with the entrails of the fish, before the fish is cooked and 

 eaten. But when these parasites occur in the flesh, their removal is 

 impossible. 



RhyncJiohothrius ilisha, n. sp., is the first example of an Indian Ces- 

 tode whose life-history has actually been worked out. It is true that 

 in the cosmopolitan forms of tapeworms, such as Taenia solium, Taenia 

 serrata, etc., the life-history is well known. In India, owing to the 

 occurrence of these species in. precisely similar hosts, the same life-his- 

 tory has been inferred ; but so far as w^e are aware no experimental 

 work of this kind has been attempted. 



Shipley and Hornell (4) described two species of tapeworms from 

 Carcharias gangeticus (now Carcharinus gangeticus) obtained in Dutch 

 Bay, Ceylon (salt water), 3rd January 1905, viz., Tertrarhynchus peri- 

 deraeus and Tetrarhynchus gangeticus. Our species is totally dissimilar 

 to the former and differs in the following particulars from Tetra- 

 rhynchus gangeticus : — 



1. Our worms are 17 times longer. 



2. A distinct neck is present. 



3. The arrangement of the proboscis tubes is quite different. 



4. The hooks are different. 



As nothing has been stated by the authors regarding the anatomy 

 of their species we have no means of carrying the comparison further. 

 Our species is quite different from other species of this genus. 



Four species of Cestoda have now been recorded from this shark, 

 viz., Tetrarhynchus perideraeus, Rhynchobothrius ilisha, Tetrarhynchus 

 gangeticus, and Discocephalum pileatum. 



Classification. — As a result of some years' observations on the Tetra- 

 rhynchidae we are of opinion that this family requires revision, parti- 

 cularly with reference to the anatomy of the reproductive organs. 

 Fortunately, we have a fairly extensive and representative collection 



