44 ZOOLOGY. 
1. Trematoda. 
2. Planariidee. 
Sus-cuass II. Cavrrarta. 
Having a visceral cavity, the nervous system bi-radiated. Composed of 
four orders, the first having a visceral cavity instead of an intestine, the 
remaining three with two openings at the alimentary canal, at Mee 
extremities. 
a. Enterodela,* with one family : 
1. Acanthocephala. 
b. Enterodela cylindrica [Nematoidea, Rudolphi], two families: 
1. Ascaride. 
: 2. Gordiide. 
c. Enterodela plicata [Acanthotheca, Diesing|, a single family and 
parasitic genus : 
1. Linguatulide. 
d. Enterodela tenioida, one family : 
1. Nemertidee. 
The greater part of the Helminthes live in various parts of other animals, 
deprived of light, with little occasion for locomotive powers, and governed 
by circumstances of great uniformity, so that we need not be surprised at 
the simplicity of structure in individual genera, although they present a 
considerable amount of variation in the aggregate. From the mode of 
their occurrence within other animals, they have been termed Entozoa, in 
which certain external species are included. In some cases the same 
species is found in waters as well as in the interior of animals. There is 
scarcely an animal, whether terrestrial or aquatic, which does not nourish 
some of these parasites, and but few of the latter infest several distinct 
species. They have been found in beasts, birds, reptiles, fishes, insects, 
mollusea, and even in the acalephe. 
These entozoa are found, according to the species, in various parts of 
the bodies they infest, as the intestines, brain, bronchie, liver, kidneys, 
muscles, blood, and bones. 
I. HetmintHopuyta. 
a. Cystica. 
These are named from the resemblance of the posterior part of the body 
to a bladder, a part which is filled with fluid (pl. 77, fig. 29). This is 
fibrous and sensitive, at times as large as an egg, and it sometimes forms 
part of several individuals. In Ccenurus the head or heads are each 
attached to a short neck; they are sub-globular, crowned with hooks, and 
have suckers arranged around the convexity, to enable it to attach itself 
to the substance whence it derives its nourishment. It lives in the brain 
and spinal nerve of sheep, and more rarely in the brain of oxen, destroying 
parts of it, and giving rise to a fatal disease, called by the expressive name 
of “ staggers,” from its chief symptom. 
In Echinococcus (called Acephalocyste by the French) there is no head 
* This name is inadmissible, having been previously used by Ehrenberg in the Infusoria, 
. 24. 
. 248 
