Page:Tropical Diseases.djvu/915

XLV] Synonym.—Tœnia asiatica. History.—Davainea asiatica was described by Linstow in 1901, from a specimen in the Zoological Museum of the Imperial Academy of Science in St. Petersburg. It was passed by a man in Aschabad (Asiatic Russia, near the northern frontier of Persia), and preserved by Anger. The parasite(Fig. 203).— The specimen examined by Linstow measures 29'S cm. in length, and is composed of 750 segments. The scolex is missing. The proglottides are all broader than long, measuring 0.16 mm. in width at the proximal end, and 1.78 mm. at the distal end. The posterior margin of each segment extends over the anterior margin of the next following segment. The genital pores are unilateral and open in the proximal third of each proglottis. The testicles (35 to 44 μ in diameter) are arranged in a ventral and dorsal layer of about eight rows each. The vas deferens extends in convolutions about one-third across the segment; the cirrus pouch is pyriform; the ovary extends across the segment between the ventral canals. The vagina forms a large fusiform receptaculum seminis. The uterus breaks up into 60 to 70 egg-balls in each segment. Mature eggs were not observed. The cystic form is unknown.

A residence in the alimentary canal of some vertebrate animal is a regular feature in the life-history of many dipterous insects. The ova of the insect are either licked from the skin, or swallowed in the food on which they had been deposited. In this way they get transferred to the stomach, where, after a time, the larvae are hatched out and undergo development. In due course they appear in the fæces. Man is not infrequently victimized in this way, especially in tropical countries. Sometimes, until a correct diagnosis is arrived at, not a little alarm is caused by the appearance of these creatures in the stools. They are easily recognized. The ringed, cylindrical body, from ½ in. to 1 in. in length according to species, broad at one end, tapering at the other, and usually beset with little spines or hairs, is sufficiently diagnostic. (Fig. 204.)

Already we know over twenty species of diptera whose larvæ have been found in or expelled from the