288 



NEMATHELMINTHES. 



primitive bundles, the substance of which degenerates, the degeneration being 

 accompanied by an active multiplication of the nuclei. In a space of fourteen 

 days they develop, within a sac-like swelling of the muscle fibres, into spirally 

 coiled worms, around which and within the sarcolemma and its connective 

 tissue investment a clear lemon-shaped capsule is excreted from the degenerated 

 muscle substance. The young Muscle -Trichina can remain, living for years 

 within this capsule, which at first very delicate, gradually becomes thickened 



and hard by the formation of 

 other layers and by the gradual 

 deposition of calcareous matter. 

 If the encysted animal is trans- 

 ferred into the intestine of some 

 warm-blooded animal in the flesh 

 of its first host, it is freed from 

 its cyst by the action of the gas- 

 tric juice, and the rudimentary 

 generative organs, which are 

 already tolerably far developed, 

 quickly attain maturity. In from 

 three to four days after their 

 introduction the asexual Muscle- 

 Trichinas become sexual Trichinas 

 These copulate and produce a 

 brood of embryos which migrate 

 into the tissues of the host (one 

 female may produce as many as 

 1000 embryos) (Fig. 235). The 

 house rat is especially to be men- 

 tioned as the natural host of the 

 Trichina. This animal does not 

 hesitate to eat the carcase of its 

 own species, and so the Trichina 

 infection is passed on from genera- 

 tion to generation. Carcases in- 

 fected with Trichinas are sometimes 

 eaten by the omnivorous pig, in 

 whose flesh the encysted Trichinas 

 are introduced into the intestine 

 of man, and occasion the well- 

 known disease, Trichinosis, which 

 when the migration takes place 

 in numbers, often has a fatal 



FIG. 236. Filaria medinensis (after Bastian and 

 Leuckart). a, anterior end seen from the oral 

 surface ; mouth ; P papilla. &, pregnant 

 female (size reduced more than half), c, 



embryos strongly magnified. 



result. 



Fam. 4. Filariidae. Body filiform, elongated, often with six oral papillae, 

 sometimes with a horny oral capsule, with four praeanal pairs of papillae, to 

 which an unpaired papilla may be added, with two unequal spicula or with 

 simple spiculum. 



Filaria 0. Fr. Mtill. (Fig. 236). With small mouth and narrow oesophagus. 

 This genus, which is sometimes destitute of papillae, lives outside the viscera, 

 usually in connective tissue, frequently beneath the skin, and is divided by 



