Accessory sac (opening into genital atrium) usually absent. Vas deferens with an external (outside cirrus sac) and an internal (inside cirrus sac) “seminal vesicle.” Three testes in each proglottis. The eggs are round or oval with two to four distinct envelopes. In mammals and birds.
Fig. 222.—Hymenolepis nana, v. Sieb. About 12/1. (After Leuckart.)
Hymenolepis nana, v. Sieb., 1852.
Syn.: Tænia nana, v. Sieb., 1852, nec van Beneden, 1867; Tænia ægyptiaca, Bil., 1852; Diplacanthus-nanus, Weinld., 1858; Tænia (Hymenolepis) nana, Lkt., 1863.
The worm is 10 to 45 mm. in length and 0·5 to 0·7 mm. in breadth; the head is globular, 0·25 to 0·30 mm. in diameter. The rostellum has a single circlet consisting of twenty-four or twenty-eight to thirty hooks, which are only 14 µ to 18 µ in length. The neck is moderately long; the proglottids are very narrow, up to 200 in number, 0·4 to 0·9 mm. in breadth, and 0·014 to 0·030 mm. in length. The eggs are globular or oval, 30 µ to 37 µ to 48 µ; the oncospheres measure 16 µ to 19 µ in diameter, with two coats, separated by an intervening semi-fluid substance (fig. 224).
This species was discovered by Bilharz in Cairo in 1851; it was found by him in great numbers in the intestine of a boy who had died of meningitis. For several years this was the only case, until 1885, since when numerous cases have come to light. Spooner (1873) even reported a case from North America, which may, however, have related to Hymenolepis diminuta. In Europe the worm is particularly frequent in Sicily, but it has also been repeatedly observed in North Italy; it has, moreover, been reported from Russia, Servia, England, France, Germany, North and South America, the Philippines, Siam and Japan, in all over 100 cases. Notwithstanding its small size this worm causes considerable disorders in its hosts—mostly children—as it sets up loss of appetite, diarrhœa, various nervous disturbances, and even epilepsy; all these symptoms, however, disappear after the expulsion of the parasites, which are generally present in large numbers.
