PARASITES WHICH INVADE THE LIVER IOI 
or lid. They consist of a germ cell and a number of 
vitelline or yolk cells of granular consistence, destined 
to provide food for the developing germ cell. These 
pass out with the bile, and are expelled from the animal’s 
body with the feces. For their further development 
it is essential that they should fall upon or be carried 
to damp or marshy ground, otherwise they undergo 
desiccation and die. 
Incubation takes place in from one to three months, 
according to the weather and other conditions. Each 
ovum hatches out into what is known as a Miracidium, 
or ciliated embryo, from the cilia which surround it. 
This organism is somewhat pear-shaped, and is provided 
at its anterior extremity with a prominence—really a 
boring apparatus. 
It now swims freely in water till it finds a small 
fresh-water snail known as Limnea trunculata. This 
snail has a spiral grey shell, and is from 4 inch to $ inch 
in diameter, and about the same from base to apex. 
It is not found in Australia, although fluke disease 
abounds in that country. Probably another inter- 
mediate host is present there. 
The ciliated embryo now attaches itself to the soft 
parts of the body of the snail, and finally reaches the 
lung. The organism then loses its cilia, becomes 
shortened, and finally becomes encysted in the snail 
as the sporocyst. 
The sporocyst contains masses of germ cells, each 
clump of which develops into an organism known as 
the Redia. This, too, contains a number of germ cells, 
and possessesa mouth and a blind tube representing 
the intestine. It wanders to the liver of the snail, 
where its germ cells develop into about twenty Cercarie, 
which are nearest in structure to the adult parasite. The 
body is made up of an egg-shaped, flat anterior portion, 
and a tail posteriorly situated. The two suckers are 
