PARASITES OF THE ALIMENTARY TRACT 53 
hooks, and is known as the “‘ proscolex.’”’ It leaves the 
intestine, penetrates into the tissues of the host, loses its 
hooks, and becomes a vesicle, from the inner surface of 
which develops the head of the future tapeworm. This 
head has received the name “ scolex.’’ 
When the carcass or portion of the carcass of an 
animal thus infested is eaten by another animal, the 
scolex is liberated, attaches itself to the mucous mem- 
brane of the intestine, and develops a number of seg- 
ments, or proglottides. The terminal segments pass out, 
and are ingested by yet another animal, and so the 
cycle commences afresh. 
(2) The Trematodes have a flattened, oval, or lanceo- 
late body, which is non-segmented. Those which are 
parasitic belong to the Distomata—that is to say, they 
have an anterior oval sucker and a round or oval ventral 
sucker, varying in position in the different members. 
They are hermaphrodite, but individual coitus is 
essential. 
The genus Bilharzia (Bilharzia crassa) inhabit the blood. 
They are not hermaphrodite, and the male and female 
are always attached, the male lying in a groove running 
the length of the female. 
The Distomata comprise : 
(a) Distomum. 
(0) Amphistomum. 
(c) Gastrodiscus. 
(d) Bilharzia. 
The flukes are of great importance, as they inhabit the 
bile-ducts, and cause the disease known as “ liver-rot.” 
Nemathelminthes. 
These are round-worms, as opposed to the Platyhel- 
minthes, or flat-worms. The sexes are nearly always 
distinct, 
