Page:Tropical Diseases.djvu/910

854 cuff-like projection over the succeeding segment. The testes are 130-160 μ in length and 60-80 μ in breadth; the vas deferens is without a vesicula seminalis. The cirrus pouch is absent. The genital pore is situated irregularly on the lateral borders. The vagina is coiled and without setæ. The mature uterus is very compact with a median stem and numerous long, slender dichotomous branches.

Synonyms.—Tœnia nana; Diplacanthus nanus; Hymenolepis murina. History.— This minutest of the tapeworms inhabiting man was first found as a human parasite by Bilharz, in Cairo, in 1851. The following year it was described by von Siebold, who proposed to call it Tœnia nana. In 1887 Grassi identified it with Hymenolepis murina of the rat, and showed that it can dispense with an intermediary host, the larva penetrating into a villus of the rodent's intestine to become a cysticercoid, and then re-entering the canal to become transformed into the adult stage.

Zoological distribution.—H. nana is found in the brown rat (Mus decumanus), black rat (M. rattus), house mouse (M. musculus), dwarf field-mouse (M. minutus), and garden dormouse (Eliomys guercinus).

Geographical distribution.—H. nana is found in Egypt, Siam, Japan, the southern States of the American Union, Brazil, Argentine, and through-out Europe, but more especially in the warmer parts, as in Sicily, where, according to Calandruccio, 10 per cent, of the children are affected.

The parasite(Fig. 201).— The strobile vary in length from 5 to 45 mm. with the number of proglottides, which may be from about 100 to 200. The scolex is subglobular and measures 139 to 480 μ. in diameter; it is provided with a well-developed rostellum armed with a single crown of twenty to thirty booklets 14 to 18 μ. long; the suckers are globular and have a diameter of 80 to 150 μ. The neck is long. The proglottides are very short anteriorly; farther down the chain they increase in size but remain broader than long. Only the hindermost segments may equal or even slightly exceed their breadth. The maximum breadth of the proglottides is from 0.5 to 0.9 mm. The genital pores open on the left margin near the anterior border of each segment. There are three testes in each segment; the vas deferens widens to form a seminal vesicle