REARING HELMINTHES FEEDING EXPERIMENTS 



127 



of a fresh host, development taking place within the intestinal wall of 

 the definitive host. This stage may be seen after feeding rats or mice 

 with ripe proglottides of the parasite (fig. 49). 



An excellent subject for the study of the digenetic Trematodes is 

 afforded by the liver-fluke, Fasciola hepatica, which is readily obtainable 

 from slaughter-houses. Eggs, when taken direct from the uterus, are 

 in varying stages of maturity, and only a certain proportion will 

 develop in water. It is better, for this reason, to use eggs which have 



been deposited, and these are usually found in 

 large numbers in the gall-bladder of infected 

 sheep. After several weeks the miracidia, 

 which are long in shape and entirely covered 

 with hairs (fig. 44), will emerge from the shell, 

 and should now be brought into contact with 

 the intermediate host. This function is fulfilled 

 by a small fresh-water snail (LimncBus minutus, 

 fig. 50), which must be quite young and into 

 which the miracidia penetrate, shedding their 

 ciliated coat in the process. Once within the 

 body of the snail, the intes- 

 a b tine and nervous system 



undergo retrograde changes, 

 and the larvae become con- 

 verted into sporocysts. In 

 the sporocysts, redise provided 

 with an intestinal apparatus 

 are formed, and from these 

 the cercariae are developed. 

 The snails should be fed with 

 water plants, lettuce leaves, 

 &c., during the developmental 

 period. When formed, the 

 cercariae leave their host and 



swim actively about in the water, where they appear as small whitish 

 bodies. Finally, they cast their tails and, after creeping up the stems 

 of water plants, they encyst above the level of the water. 



Another subject which is easily procurable is Diplodiscus sub- 

 clavatus, an Amphistomide which is frequently present in the terminal 

 portion of the gut of frogs. The eggs when deposited contain the 

 fully formed miracidia, which soon emerge and penetrate into small 

 varieties of Planorbis. The cercariae encyst spontaneously in the 

 water or on frogs. 1 



FIG. 49. Longitudinal 

 section through a villus of 

 the small intestine of a 

 rat with a cysticercus of 

 Hymenolepls mttrina. Mag- 

 nified. (After Grassi and 

 Rovelli.) 



FIG. 50. Shell of 

 Tjimnceus minutus 

 Drap. a, Natural 

 size, b, Magnified. 

 (After Leuckart.) 



1 A. Looss, "Festschrift z. 70. Geburtst. E. Leuckarst," Leipzig, 1892. 



