HELMINTHES. 47 
oblong, suddenly tapering to a point posteriorly ; sides nearly parallel ; head 
truncate in front ; neck narrowed, eye dots two, on the narrow part, oblong 
and white, with a black dot upon the internal margin; ventral opening less 
than one third the entire length from the posterior extremity. It inhabits 
springs in eastern Pennsylvania, and feeds upon animal matter. When cut 
in two, each part becomes an entire animal. 
UL. Cavrrarta. 
a. Enterodela. 
1. The Acanthocephala, which are placed with the Parenchymata by 
Cuvier, are composed of round worms represented by the genus 
Echinorhynchus, the chief character of which is a straight, round, retractile 
trunk, armed with rows of recurved tooth-like hooks, which retain it in 
place when thrust into the intestines. A small pore is sometimes 
observable at the end of this trunk, but it is probable that nourishment is 
absorbed by its entire surface. A vascular tube runs longitudinally on 
each side, and is lost towards the posterior extremity. These noxious 
animals seem not to have been found in man, although numerous species 
infest vertebrate animals. They sometimes bore through the intestines, and 
pass into the cavity of the abdomen, and into other parts of the body. 
Echinorhynchus gigas (pl. T7, fig. 39) is from three to fifteen inches long, 
and infests hogs, especially such as are confined to be fattened. 
b. Enterodela cylindrica. 
1. The Ascarzde include various genera of internal parasites, of which 
the genus Ascaris is among the best known, and contains slender, round 
worms, tapering towards both ends. The head is provided with three little 
valves, between which the mouth is placed. The intestine is straight, the 
vent terminal, and the nervous system bilateral. Ascaris lumbricoides 
(pl. TT, jig. 41) takes its trivial name from its general resemblance to a 
lumbricus, or earth-worm. It is white, from six to twelve or fifteen inches 
long, and the female is larger and more abundant than the male. It infests 
the small intestines of man, and is frequently fatal to children, in which it 
sometimes penetrates to the stomach, and even to the mouth. As many as 
five hundred have been ejected by a child in the course of eight days. 
It is sometimes discharged from abscesses in the abdomen, and it has 
rarely been passed from the bladder. This species infests the hog and the 
ox, and an allied one (once considered the same) is found in the horse. 
Owen, some years ago, calculated the number of eggs in a female of this 
species to exceed sixty millions. Gluge and Mandl found eggs of an 
Ascaris, without the animal, in the lungs of frogs, supposed to be introduced 
with the air. 
Oxywris vermicularis, Linn. (pl. 77, jig. 42), is half an inch long, 
cylindrical, with the posterior portion subulate. It infests the large 
intestines of children. 
Trichocephalus dispar (jig. 40) is found with the preceding species, and 
differs in having the anterior extremity attenuated like a thread, and 
resembling the lash of a whip, of which the posterior end would be the stock. 
It is one or two inches long, of which the thick part occupies about a third. 
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