Oxyuris vermicularis.-A small thread-worm infesting the rectum, especially in children, causing much annoyance by its nocturnal. wanderings. Sometimes found in the nostrils.

The male is less than a quarter of an inch in length; the female about double that size.

Oxyuris is characterised by a body of fusiform shape, terminating in a tapering tail.

The drawing represents Oxyuris vermicularis.

Oxyuris vermicularis. A. Head of the parasite, more highly magnified.
B. The entire worm, magnified 100 diameters. œ. Esophagus. S.
Stomach. i. Intestine. o. Oviduct. u. Uterus. a. Anus.

Filaria bronchialis, or Strongylus bronchialis, is found in the bronchial tubes of man, and, when accumulated in vast numbers, is capable of causing suffocation.

R

In the lungs of the sheep a variety of this worm is frequently found occupying little tuberculous-looking spots, commonly mistaken for tubercle (from which the lungs of the sheep appear to be perfectly exempt). The young of the parasite migrate to the small bronchial tubes, and occasion considerable irritation.

The drawing represents one of the so-called tubercular masses from the lung of a sheep, and shows the worm coiled up amidst a quantity of exudation matter, undergoing calcareous degeneration.

In calves Filaria are very common, producing the disease known as 'husk,' from the constant cough which is present.

Filaria oculi.-Minute specimens of these worms have occasionally been met with in the crystalline lens and the anterior chamber of the eye, floating in the aqueous humour. The parasites appear to occur most frequently in the eye of the horse, although now and then they are met with in the human subject.

The structure and development of the worm have not been satisfactorily made out, but some of the best authorities consider it to be the sexually immature young of some Filaria that has migrated to this position.

Filaria Medinensis, or Guinea Worm, occurs only in the tropics. It is found most frequently beneath the skin in the cellular tissue of the legs, although in the natives of Hindostan, who wash after defæcation, it is occasionally found in the neighbourhood of the genital organs, and also between the shoulders of water-carriers, who transport their burdens in skins on their backs..

Nearly the whole of the worm is occupied by the uterus, which is generally filled with the young ones, which are distinguished by their thin tapering tails, as shown in the drawing.

The female worm only is known, and reaches an average length of three feet, although it is stated to vary from one foot to ten or twelve feet. The body is cylindrical, tapering at both ends, and about one-eighth of an inch in thickness.

The young of the Guinea worm inhabit pools and marshy places, and find entrance into the human body, not by the mouth, but by boring through the skin, or entering some of the follicles. Once located there, they grow with rapidity, attaining their full length in from five to ten months, about six being the usual time,

Strongylus gigas is a large species of round worm infesting the kidneys of man and some of the lower animals. The female grows to the length of two or three feet, the male to a foot long ; the colour of the worm is reddish. Of its mode of reproduction nothing certain is known.

Strongylus paradoxus is found in the bronchial tubes of the pig. The female worm is about one inch and a half long, and is peculiar from the constant protrusion of numerous coils of the reproductive organs, filled with eggs and embryos, many of them living, from different parts of the body; sometimes the aperture is near the head, and sometimes close to the tail, and occasionally there are two or three openings in the same worm.

The male worm is smaller than the female, and is known by the bursal appendage at its tail and its long double hairlike penis.

Trichocephalus dispar, well known by the name of the whipworm, from its peculiar form, is found principally in the human cæcum. The worm varies in length from an inch and a half to two inches; the neck is double the length of the body, and much less in diameter, being, indeed, a mere filament.

For some time the opinion obtained that the Trichocephalus dispar was the mature form of Trichina spiralis; this is now known to be erroneous.

The illustration shows the Trichocephalus of its natural size and magnified.

3

Fig. 204.

Trichocephalus dispar.

Trichina spiralis.-Much interest attaches itself to this parasite, in consequence of the extraordinary prevalence of the young brood in the muscles of the pig, from which, unfortunately, it is easily transferred to the intestines of man. After this migration the worm rapidly attains sexual maturity, and develops a number of embryos, which immediately wander from the intestines to the muscles, so that in a very brief period almost every voluntary muscle in the body becomes infested.