206 ASSOCIATION OF ORGANISMS—THE WEB OF LIFE 
gigas, fig. 1154), which, when adult, lives in the intestine of the 
pig, maintaining a firm hold by means of a formidable hollow 
“ proboscis”, thickly studded with hooks. The eggs pass out of 
the body of the pig, and some of them are swallowed by beetle- 
grubs, within which the development is carried on to a certain 
stage. If an infested grub happens to be eaten by a pig the life- 
history of the parasite is completed. 
ANIMALCULES (Protozoa) AS PARASITES 
The large group of Gregarines (Sporozoa) includes typical 
internal parasites, in which the body is surrounded by a firm 
elastic membrane, through which the body-fluids or digested food 
of the host are easily 
absorbed. A well-known 
form (Clepsidrina 6blat- 
tarum, fig. 1155) infests 
the intestines of the 
cockroach. The young 
parasite is worm-like 
in shape, and its body 
is divided into three 
regions, one of which 
bears hooks, and serves 
Fig. 1135.—Cockroach Gregarine (Clepsidrina blattarum), enlarged ao tes of adhesion 
to various scales. a, Young gregarines attached to cells of intestine; tO the host. Later on 
Band ¢, later stages lying free within intestine: D, spore-cyst in section, < é 
x, 2, 3, Three body-regions, of which x is thrown off by adult; 7., this part is thrown off, 
mest peste rere 2 eee es mene cud the: pregarine: Mes 
freely in the intestine, 
where it absorbs food, and increases considerably in size. The 
life-history is somewhat peculiar. Two parasites adhere together, 
and become enclosed in a firm case or cyst, which is passed out 
of the body of the host. If the surroundings are sufficiently damp 
the outer part of the cyst swells up into a gelatinous layer, and 
complex changes go on in the interior. The bodies of the two 
contained parasites break up into a large number of minute spores, 
with firm coats, scattered through a kind of net-work. A number 
of tubes are also formed which turn inside out, and since they 
convey the spores out of the cyst are termed sforoducts. If 
these spores are swallowed by a young cockroach their firm coats 
