BRANCHIURA FROM LAKE TANGANYIKA. 281 



specimens of the Tanganyika Serranid Laies microlepis also 

 usually bore some examples attached to the surface of the head 

 or within the mouth-cavity. 



It is commonly considered that these parasites do not constitute 

 a menace to the fish on which they prey. This was equally the 

 impression made in the present instance. Cases have been 

 recorded, however, in which it seems clear that an excessive 

 number of Argulids infesting a fish may actually cause the 

 death of their host. What appeared to be a striking instance of 

 this came to my notice during this Expedition, and certainly 

 merits a few words of description. Nearing the north-eastern 

 shore of Tanganyika one aftei'noon, after a long voyage, a large 

 fish was noticed floating on the surface of the water. My men 

 fetched it on board, and it proved to be a specimen of the 

 " kavungwe " {Auchenoglanis occidentalis, var. tanganicanus), 

 absolutely covered with Argulidfe. There was liteiully hardly a 

 spot on the body not infested with the parasites, and in the head 

 region and within the mouth they were positively overlapping 

 and lying on top of one another. Instead of detaching isolated 

 specimens, as had usually to be done, a layer of writhing Argulids 

 could be scraped from most parts of the body. The fish was not 

 only perfectly fresh, but was still feebly making convulsive 

 movements, and one could not resist the conviction that it was 

 succumbing to the fierce attack of such a swarm of parasites. 

 The latter, in this instance, did not all belong to one species. 

 There were specimens of both Ai-gulus striatus and A. incisus, 

 the last-named species, strange to say, being obtained on this 

 occasion only. 



It was no very unusual thing on Tanganyika to discover the 

 bodies of large fish floating far from shore. The crew of my dhow 

 kept a sharp lookout, and made a point of picking them up when 

 possible, as it meant a little addition to their fare, unless the 

 fish were too putrid for even their taste. I never saw Argulidse 

 under these circumstances, except in the case detailed above, 

 but in no other instance was the fish still living. The suggestion 

 nevertheless occurs, that these also may have been victims of 

 such parasites as appear to have caused the death of the 

 Auchenoglanis. 



No doubt, as is usually the case, the difi"erent types of Argulid 

 are not rigidly confined to one host, though they may have a 

 pi'eference for a particular fish. Thus Argtdus ritbropitnctatus, 

 taken on difierent occasions and in different localities, was 

 obtained only from Lates microlepis ; similarly, A . rubescens was 

 found only on Chrysichthys hrachynema. On the other hand, 

 A. striatus, perhaps the commonest and most widely distributed 

 Tanganyikan form, was obtained from a number of hosts, whilst 

 A. africanus and Dolops ranarimi, owing to their extended 

 - distribution, clearly have still larger host-lists. 



The question suggests itself — do • the Tanganyika endemic 

 species infest endemic fish ? Since the number of endemic types 



Pnoc. ZooL. Soc— 1913, No. XIX. 19 



