some molluscs of natal lagoons. 279 



Inhabitants of Eivers Found in Natal Lagoons. 



Alter the rains I liave found numerous inhabitants of semi- 

 stagnant pools washed downstream, attached to floating vegeta- 

 tion or lying on the sand-bank at the mouth of the rivers. Many 

 others can be found breeding on the water-lily leaves or rushes at 

 the edge of the lagoon where the water is not too salt. 



On the sand-bank at the mouth of the Amanzimtoti Eiver I 

 found Physopsis africana and Limncea natalensis, which had 

 been washed downstream. The latter was found breeding all the 

 way up the river and, in places, was associated with Ancylus (two 

 varieties), Isidoia for.shaU and small Planorbis. 



At the mouth of the Umbogintwini river I found numerous 

 Limncea yiaialensis crawling about on the sand at the water's edge 

 and, at the stagnant part of the lagoon, I foiuid PlanorJitH 

 pfcifferi breeding on water-lily leaves. 



From an overflow pool close to tlie lUovo lagoon I have 

 collected Planorbis pfciffcri, Scgnioitina pJanodiscus, Isidora (pro- 

 bably tropica) and AncyJiia. 



On the Tongaat beach I have found numerous Ancyli attached 

 to the rocks over which a. small rivulet was breaking into the 

 sea. 



Some fresh-water inhabitants from a stream along the course 

 of the river at Karridene^P /?7/so/)s/s, Planorbis pfciffcri, and 

 Jjinmcea natalensis — ware rapidly killed when placed in a bottle 

 containing lagoon water and brackish water inhabitants. 



Physopsis afrvHina is tlie common intermediary host of 

 SchistosoiniDn hieniatobiiiin, S. niansojii and S. bovis in Natal. 

 Limncea natalensis is sometimes heavily infested with Cercaria 

 piijmcntosa, the larval stage of Fasciola gigantica, and Porter has 

 found it infested with Fasciola licpatica at times. Isidora tropica 

 and Isidora forshali are sometimes infested with Amphistomes, 

 whilst Planorbis pfciffcri is commonly infested with cystophorous 

 and other cercarite. All these common inhabitants of Natal rivers 

 are occasionally infested with Schistosoines. It is interesting to 

 note that neither the cercariae themselves nor their intermediary 

 hosts can survive for any length of time in the brackish water 

 that is generally present in the lagoons of Natal. 



These investigations have been carried out under the auspices 

 of the StreatfieM Research Fimd of the Eoyal Colleges of 

 Phvsicians and Surgeons. 



w 



