THE ECHINORYNCHUS. 123 
Order 1. Acanthocephali.—These are aberrant Nematode 
worms (sometimes referred to a separate class), without any 
mouth or digestive tract, but with an extensible spiny beak, 
living by imbibition of the fluids of the alimentary canal of 
their host. : 
The thick subcuticula is penetrated by a network of ves- 
sels, whose trunks form two oval bodies of unknown use 
called lemnisci, which hang down free in the body-cavity. 
The sexes of Echinorhynchus are distinct. The eggs are 
usually spindle-shaped. The embryo develops in the body 
of the parent worm, and is surrounded by several membranes, 
with a circle of hooks arranged bilaterally around the mouth, 
‘The embryo contains an oval mass of nuclei, being the ru- 
a aceasta Mae gee ne 
diments of an intestinal canal. Finally it passes into 
some crustacean or insect, in whose body it becomes so far 
developed, that when its host is swallowed by some vertebrate, 
such as a fish, the embryo is liberated in the intestines of the 
second (vertebrate) host and soon attains sexual maturity. 
Nearly a hundred species are known. 
Echinorhynchus gigas, the female of which is 50% centime- 
tres (20 inches) in length, lives in the small intestine of the 
pig. Its eggs pass out, becoming scattered on the ground, 
where they are eaten by the white grub or larva of the Euro- 
pean cockchafer. The egg-membranes burst in the stomach 
of the grub, and the embryos thus liberated penctrate, by 
