286 



NEMATHELMINTHBS. 



whip-shaped : posterior part cylindrical and sharply distinct, enclosing the 

 generative organs, curved in the male. Lateral lines absent. Main median 

 lines present. The penis is slender and furnished with a sheath, which is turned 

 inside out when the former is protruded. The hard-shelled, lemon-shaped eggs 

 undergo the first part of their development in water, without intermediate host. 

 Tr. dispar Rud. In the human colon : these worms do not live free in the 

 intestine, but bury their filiform anterior extremity in the mucous membrane 

 (Fig. 234). The eggs pass out of the host with the faeces, as yet without a sign 

 of beginning development, which only takes place after a prolonged sojourn in 

 the water or in a damp place. According to the experiments of Leuckart, 

 performed with Tr. affinis of the sheep and Tr. crenatus of the pig, embryos 

 with the egg membranes, if introduced into the intestine, develop into the adult 

 Trichocephalus ; and we may therefore conclude that the human Tr. dispar is 



introduced directly, and with- 

 out an intermediate host, either 

 in the drinking water or in 

 uncleaned food. The young 

 Tr. dispar is at first hair-like, 

 and resembles a Trichina, and 

 only gradually acquires the 

 considerable thickness of the 

 hind end of the body. 



Trichosomum Rud. Body 

 thin, hair-like, but the pos- 

 terior end of the body in the 

 female is swollen. Lateral 

 lines and the principal median 

 lines are present. The male 

 caudal extremity has a cuta- 

 neous fold and a simple penis 

 (spiculum) and sheath. Tr. 

 muris Creplin., in the large 

 intestine of the house-mouse. 

 Tr. crassicauda Bellingh., in 

 the bladder of the rat. 

 According to Leuckart, the 

 dwarfed male lives in the 



uterus of the female, and there are usually two or three, more rarely four or 

 five males in a single female. There is also a second species of Trichosomum 

 found in the bladder of the rat, Tr. Schmidtii v. Linst., the larger male of 

 which was formerly taken for that of Tr. crassicauda. 



Trichina Owen. * Body thin, hair-like. Principal median lines and lateral 

 lines are present. The female generative opening well forward. The hind end 

 of the body without spicule ; with two small conical papillae, between which 

 the cloaca projects. 



Tr. spiralis Owen, in the alimentary canal of man and numerous, principally 

 carnivorous, mammalia ; hardly two lines in length. The viviparous females 

 begin to bring forth embryos about eight days after their entrance into the 

 alimentary canal. These embryos traverse the intestinal walls and body cavity 

 of the host, and migrate, partly by their own movements in the bundles of 



* Compare the writings of R. Leuckart, Zenker, R. Virchow, Pagenstecher, etc. 



FIG. 234. -Trichocephalus dispar (after R. Leuckart). 

 a, egg. b, female, c, male with the anterior part of the 

 body buried in the mucous membrane ; Sp spiculum. 



