HABITS OF FLUKE-WORMS. 109 
occurring in the liver of asingle sheep. At this time it passes 
into the intestine, and thence is carried out with the excre- 
ment. The eggs or flukes in many cases drop 
into pools, ditches, or ponds ; here the cili- 
ated young (like Fig. 69) is liberated. Its 
body is spindle-shaped, with a double eye- 
spot. Itis very active, and soon after birth 
enters the body of a snail (Limneus), 
where it transforms into a large sac, and 
develops new larve in its interior. This 
sac-like larva is called a ‘‘ nurse,” ‘‘sporo- 
cyst,’”’ or, when more highly developed, a 
*‘redia.’”? The progeny of the redia is 
termed a ‘‘cercaria.’”’ The cercarie# are 
restless, migrating from the bodies of their 
snail-host, and have been known in a few 
instance to penetrate the skin of human 
beings. They are probably more usually 
: : Fig. 71. — Fasciola 
swallowed by sheep and cattle while drink- hapa enlarged. , 
: : : hed intestine.— 
ing or grazing, when snail-shells may be Fe ope a ean 
accidentally swallowed. From the diges- Bene’ 
tive canal of sheep, etc., the cercaria penetrates into the 
liver, where it probably loses its tail and becomes encysted, 
after many weeks or even months becoming a sexually ma- 
ture distome. From the liver it passes out through the 
liver-ducts into the intestine, and is finally expelled, thus 
completing its cycle of life. 
Distomum lanceolatum Mehlis differs from Fasciola he- 
patica in the intestine being simple and forked, while that 
of the latter is much branched. It has occurred but three 
times in man, but is not rare in the sheep and ox. It has 
been detected in Europe in the pig, deer, rabbit, and hare. 
Two immature Distomes have been found in the human 
eye, and Cobbold thinks they may both be the young of 
D. lanceolatum. It is described by Diesing under the name 
of Distomum ophthalmobium, is half a line in length, and 
occurred between the lens and its capsule, appearing as dark 
spots on the surface of the lens. Distomum crassum Busk 
and D. heterophyes Siebold have each been only once 
