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XLV] its resemblance to Ascaris lumbricoides it has been taken for miniature specimens of that species. The males are 50 mm., the females 55 mm. in length, and 2-3 mm. in breadth. The posterior end tapers rapidly in the female, terminating in a sharp point. The mouth has a cuticular cuff and two lips provided with papillæ and teeth. The bursa is bladder-shaped with pedunculated external papillae and unequal spicules. The female has two ovaries and vulva situated anteriorly.

Dr. King, of St. Lucia, forwarded some specimens of this parasite in copula to Leiper; they are said to have been coughed up by a woman. Copulation is permanent, males and females being found adherent to one another. The male has two equal spicules and the caudal bursa is provided with many ribs; the mouth is large and terminal, leading into a dilated buccal capsule, at the bottom of which there are six sharp teeth.

Leiper was first of opinion that the parasite was near to S. trachealis of poultry, and an accidental occurrence in man. Further examination has convinced him that it is probably a new species more nearly related to the members of the genus found in mammals, but more especially to S. dispar of the puma (Felis concolor).

Synonyms.—Anguillula stercoralis; A. intestinalis; Leptodera stercoralis; L. intestinalis; Rhabdonemaintestinale.

It sometimes happens that, while searching the fæces for the ova of the ankylostomum, the observer is astonished by seeing a small, snake-like animal (Fig. 185) suddenly rush across the field of the microscope. On careful examination, this animal is found to be about 0.2 mm. or 0.3 mm. in length by 0.013 mm. in breadth; to have a sharply pointed tail and a rounded head; to be transparent; and to exhibit a short œsophagus which terminates in a double œsophageal bulb, the posterior end of which is provided with three tooth-like segments. This is the larval form of Strongyloides stercoralis. Strongyloides stercoralis was discovered by Normand in 1876. For a time it was supposed to be a cause of a form of chronic diarrhœa very prevalent in Cochin China. Later investigations, while clearing up the natural history of the parasite, have robbed it of any claim to pathological importance. It has been found that, though not so common, its geographical distribution is about coextensive with that of Ankylostomum duodenale, and that the physical conditions demanded for the non-parasitic stages of these two worms are about the same. Powell found it in India in about 15 out of every 20 cases of anæmia.