240 UNSEGMENTED WORMS 



wasp, whence their larvae bore into the intestine and eventually 

 emerge. 



4. The larvae are parasitic in one animal, the sexual adults in another 

 which feeds on the first. Thus Ollulanus passes from mouse 

 to cat, Cucullanus from Cyclops to perch. 



There are other life-histories, and many degrees of parasitism. The 

 most remarkable form is Angiostomum (or Ascaris or Leptodera) 

 nigrovcnosum. In damp earth males and females occur, the progeny of 

 which pass into the lungs of frogs and toads. There they mature into 

 hermaphrodite animals (the only example among Nematodes), which 

 produce first spermatozoa and then ova. They are self-impregnating, 

 and the young pass out into the earth as males or females. Here there 

 is alternation of generations : and a somewhat similar story might be 

 told of Rhahdonema strongyloides from the intestine of man, and 

 Leptodera appendiculata from the snail. 



There are several quaint reproductive abnormalities, thus — the 

 female SphcBvularia bonibi, which gets into the body cavity of the 

 humble-bee, has a prolapsed uterus, larger than itself : the male of 

 Trichodes crassicauda passes into the uterus of the female. 



Parasitic Nematodes 



Trichinella (Trichina) spiralis is a formidable parasite in man, pig, 

 and rat, but it has been introduced experimentally into hedgehog, 

 fox, dog, cat, rabbit, ox, and horse. The sexual forms live in the 

 intestine, the female about 3 mm. in length, the male less than half 

 as long. After impregnation the female brings forth numerous embryos 

 viviparously, sixty to eighty at a time, and altogether about 1500. 

 These are produced in the wall of the intestine, or in the adjacent 

 lymphatic spaces. Most of them find their way into lymph and blood 

 vessels, and are swept by the blood stream to the muscles ; occasion- 

 ally some seem to migrate actively, boring their way especially through 

 connective tissue. The migration causes inflammation and fever. In 

 the muscle fibres they grow, coil themselves spirally, and become 

 encysted within a sheath, at first membranous and afterwards cal- 

 careous (Figs. 131 and 132). The cyst is partly due to the muscle, 

 and partly to the parasite. The infected muscle fibre degenerates. 

 In these cysts, which may be sometimes counted in millions, the 

 young Trichinae remain passive, unless the flesh of their host be eaten 

 by another — pig eating rat, man eating pig. In the ahmentary canal 

 of the new host the capsule is dissolved, the embryos are set free, and 

 become in two or three days reproductive. The male seems to die 

 after copulation. 



Among the numerous other parasitic Nematodes the following may 

 be noted : — The giant pahsade worm {Eustrongylus gigas) occurs in the 

 renal region of domestic animals, etc. ; the female may be 3 ft. long. 

 The armed palisade worm {Strongylus armatus) occurs in the intestine 

 and intestinal arteries of horse, causing aneurysms, colic, etc. The 



