SOUTH AFRICAN CI^RCARL^:. 



By F. G. Cawston, INI.D. Cantal 



Read July y, lynj. 



A study of the x-arious cercaricG that have been descriljed in 

 Sotith Africa shows that they are mostly distome or amphistome 

 larv?e. There are several distinct species cf furcocercous 

 cercarict, a large \ariety of leptocercons ones, a trichocercoiis 

 cercaria, and possiljly a few microcercous forms. Eye-spots 

 occur in some of the leptocercons and furcocercous varieties. 

 Without exception the larval hosts are fresh-water molluscs. 

 Amphistomes have been observed encysting. 



The (jccurrence oi two cercaria? species in the same host 

 indi\idual is not uncommon. On several occasions I have found 

 two distinct furcocercous forms in the same mollusc ; on other 

 occasions, the same indi\4dual mollusc was infested with Ijotli 

 leptocercons and furcocercous cercaria. 



The classitication of the distomes is a somewhat ditiicnlt 

 problem until more of the life-histories have been worked out. 

 So far, we are sure of the life-cycle of Dlstoiiui hitcnm and 

 Schistosonniiii lucnialobiiiin alone. 



In " .V liidlogical Survey of the Descril^ed Cercarise in the 

 United States," which ap])eared in " The American Naturalist," 

 Vol. Uni. Jan., lyiy, 1^. C. Faust described 8i different species 

 of cercari;o. tlie life-history of only one of which had been 

 ascertained. 



It is im])ortant that the distinctive points of the various 

 cercari?e be carefullv recorded, and. where possible, compared 

 with the structure ( f adult flukes. In the " Illinois Biolo,gical 

 Monograi)hs," Vol. I, .\pril, iyJ5. W. W. Cort observed: "A 

 combination of adult characters \\'ill often give a clue to the 

 family, or even in a few cases to the genus, to which the cercaria 

 belongs. Allowance must be made, however, for the fact that 

 adult characters may be somewhat m( dihed in the development of 

 the cercaria." 



Heavy Infestation. 



There is a distinct increase in fluke-infested molluscs at 

 certain seastjns of the year. It would seem that heavily- 

 infested molluscs die sooner than molluscs which do not harbour 

 cercarias, and infested specimens are more diflicult to keep alive 

 under artificial conditions. 



