igij-] T. Southwell : Parasites from Fish. 95 



Wallago atht occurs throughout India, Ceylon and Burma. If 

 Mahseer is a normal host of this parasite, then two hosts are now 

 known. The host, or hosts, in which the earher larval stages, 

 sporocyst, redia and cercaria, occur, have still to be discovered. 



Wallago attu is an exceedingly voracious fish and doubtless feeds 

 amongst other species on Nandus niarmoratus. It is possible that 

 the mature Distomid described from Wallago attu may be the adult 

 of the young Distomid described in this paper from Nandus niar- 

 moratus. The principal and only obvious differences lie in the 

 fact that in the young form of this worm the gut is not sinuous, 

 but this may become so when the parasite becomes adult. In 

 that case the Mahseer {Barhus tor) becomes a collateral host only. 



An immature Trematode from the ovaries of Nandus niarmora- 

 tus, Ham. Buch. 



** Distomum *' sp. 

 (PI. ix, figs. 13—14-) 



During the examination of a number of specimens of Nandus 

 niarmoratus, Ham. Buch., a freshwater fish seldom exceeding 7 

 inches in length, from the Bhagirathi river at Berhampur Court, 

 Bengal, India, on June 30th, 1912, large numbers of immature 

 Trematodes were discovered parasitic in the ovaries. 



No examples were found in the male fish examined, the para- 

 sites being limited entirely to the females. This fish spawns in 

 the various rivers be3^ond tide-marks, between the middle of June 

 and the middle of August. The diameter of the eggs is approxi- 

 mately '5 mm. The parasites were found adherent by their ventral 

 sucker to the eggs of the fish. Not more than one parasite was 

 found attached to each egg, and roughly, not more than 10 per cent 

 of the eggs were aft'ected. The parasites were not easy to detect, 

 being of exactly the same colour as the eggs of the fish, viz. yel- 

 lowish brown. Other specimens of the parasite were found 

 attached to the mesentery and to the stroma framework of the 

 ovary. There can be no doubt but that such eggs as are attacked 

 by this parasite are eventually destroyed, and it appears probable 

 that the output of eggs is thus decreased by approximately 10 per 

 cent. Infection appears to be highest when the eggs of the fish 

 are almost ripe, and this serves the double purpose of providing 

 a maximum of food for the parasite, as well as ensuring its protru- 

 sion and liberation with the ripe eggs. Opportunity is thus 

 afforded the parasite of finding its final host and maturing therein. 



Description of the parasite. 



I^ength of the longest specimen . . 4 mm. 



Length of the smallest specimen . . 2 '8 mm. 



Breadth of the longest specimen . . i"3 mm. 



Breadth of the smallest specimen . . i mm. 



The body is superficially divided into two parts. The anterior 

 ith is subglobular and the posterior -|ths is flat and leaf-like. They 



