Fig. 67.—Ascaris lumbricoides.—1, complete worm, 2, head, 3, tail of the male, 4, middle of the body of female.
The Ascaris lumbricoides is a large round worm which attains the size of a quill pen, and which is commonly found in the stomach or the lesser intestines of children when in good health. Aristotle was acquainted with it. It has been observed throughout Europe, in Central Africa, in Brazil, and Australia. The same species lives in the intestines of the pig; but the Ascaris megalocephalus, which is usually found in the horse, is of a different species.
The Ascaris acus of the pike lives at first in a common white fish, the Leuciscus alburnus, and passes with this fish, which serves it as a vehicle, into its final host.
Another common nematode, the Oxyurus vermicularis ([Fig. 69]), a parasite of man, is a small worm of the size of a fine pin, which often multiplies in the rectum of children, causing intolerable itching. It is by means of their microscopic eggs that they penetrate into the system; these are hatched in the stomach, and are completely developed at the end of eight or ten days. They pass from the anus in great numbers.
Fig. 68.—Trichocephalus of man.—1, female, a, cephalic extremity, b, caudal extremity and anus, c, d, digestive tube and ovary, e, orifice of sexual apparatus. 2, isolated egg. 3, male, a, cephalic extremity, b, anus, c, digestive tube, d, spicula or penis, e, sheath into which it is withdrawn.
