3/6 SOUTH AFRICAN SNAILS. 



koi. These developed mostl}- in rcdise, which i>ossess lateral 

 ap]:)endages and have the appearance of lizards as they move. 



Cercaria catenata, a chained form, occurs at Durfhan, 

 Magalieshurg, and Potchefstroom. Cercaria arcuata, whose 

 chains join, posterior to the ventral sucker, infests specimens of 

 Isidora schakoi at Klerksdorp. 



Isidora schakoi, at the Potchefstroom Golf Links is heavily 

 infested with an eye-spotted cercaria, Cercaria frondosa. The 

 eye-sjjots branch in fully developed cercariae, and present the 

 appearance of leaves. In some, the pigment is continued down on 

 either side of the gut, as though connected with an elementary 

 nervous system. The eye-spots are visible through the walls of 

 the rediae. in which the cercariae develop. 



So far, the life-history of the Bilharma is the only one that 

 lias l)een completed. No one has yet identified the cercaria which 

 gives rise to '" liver rot " in South African sheep. The cercaria 

 is a leptocerojus form developing in rediae, and I am of opinion 

 that Limncca nataiensis is its usual intermediary host, not 

 Limtuca truncatida, as formerly supposed. It is a revolting sight 

 to see these leaf-like liver-flukes crawling about the bile-ducts of 

 infested South African sheep. 



Cercaria attacks any portion of the skin ; though infection 

 was found to take place most readily by the mouth in Venezuela, 

 the Japanese believe cutaneous infection to be the commoner. 

 By means of tiny boring processes around its oral sucker, the 

 cercaria is able to bore its way through the skin or mucous 

 membrane. 



Paragomius ivcstcrmanii, which develops from a tadpole 

 cercaria in Japan, inhabits the lung capillaries of man. Should 

 expectoration containing its eggs reach fresh water, a ciliated 

 miracidium emerges from the shells and attacks Mclania libcr- 

 tina, the common fresh-water mollusc, which acts as its inter- 

 mediary- host. 



The various members of the Schistosome group inhabit 

 various parts of the blood-stream, and live in their human host 

 for many years. Unlike the smaller blood-parasites, which are to 

 be found in the general circulation, they are confined to certain 

 of the bigger blood-vessels. Schistosomiim mansoni and Schis- 

 tosomum japoiiicuui have chosen the small blood-vessels of the 

 intestinal wall. The eggs of Schistosoinuni mansoni have a 

 lateral spine, which assists in their escape through the intestinal 

 wall. Sometimes, however, the eggs become loose in the blood- 

 stream, and they cause paralytic symptoms from their presence 

 in the spinal circulation of some Egyptian patients. 



The " seat of selection " of Schistosomum. hccmatobiinn is 

 the bladder-wall, where the parasites burrow their way into the 

 smallest veins that can accommodate them. As the bladder 

 distends, these spine-pointed eggs rupture the vessel-wall, and 

 escape with the urine. The mixacidium, which escapes in fresh 

 water, attacks Physopsis africana, its intermediary host. 



