460 CLASS ECHINODERMATA. 
One or two inches in length, of which the thick part occupies 
only one third. In the male this part is convoluted spirally, 
and a small penis is visible, which comes out near the tail. 
In the female it is straighter, and simply pierced at the ex- 
tremity. 
It is one of the most common worms in the large intestines 
of man, and multiplies beyond measure in certain disorders. 
From the trichocephali have been distinguished, 
TRICHOSTOMUS, Rus. CAPILLARIA, Zeder., 
The anterior part of which grows slender only by degrees ; 
and the 
OxyYuRIS, Rud., 
In which it is the posterior part of the body which is atten- 
uated in the form of a thread. 
A species is known belonging to the ccecum of the horse, 
Oxyuris curvula, Rud. Getz. vi. 8. Encyc. xxxiii. 5., from 
one to three inches in length. 
CUCULLANUS, 
Have the body round, more slender behind ; the head blunt, 
invested with a sort of little hood, often striated ; the mouth 
round. 
These have hitherto been found only in fish. The most 
common is that of the perch. C. lacustris, Gm. Goetz. ix. 
A. 3. Encyc. xxxi. 6., which also infests the pike, &c. It is 
viviparous, about an inch in length, of the thickness of a 
thread, and appears to be red, in consequence of the blood 
with which its intestine is usually filled. 
OPHIOSTOMUS, 
With the body of the preceding, are distinguished by a mouth 
