178 MANUAL OF ZOOLOGY. 



Trichina is known in two different conditions, sexually imnia- 

 ture or mature. In its sexually immature condition it inhabits 

 the muscles, usually of the pig, in vast numbers, each worm 

 being coiled up in a little capsule or cyst. In this condition 

 the worm is incapable of further development, and may re- 

 main, apparently for an indefinite period, without change, 

 and without seeming to produce any injurious results to the 

 animal affected. If, however, a portion of trichinatous muscle 

 be eaten by a warm-blooded vertebrate, and so introduced into 

 the alimentary canal, an immediate development of young 

 Trichincs is the result. The immature worms escape from 

 their enveloping cysts, grow larger, develop sexual organs, 

 and give birth to numerous progeny, which they produce 

 viviparously. The young Trichince thus produced perforate 

 the walls of the alimentary canal, and, after working their 

 way amongst the muscles, become encysted. If the animal 

 in which these changes go on has sufficient vitality to bear 

 up under the severe symptoms which are produced by the 

 migration of the Trichina, he is now safe ; since they can- 

 not become sexually mature, or develop themselves further, 

 until again transferred to the alimentary canal of some other 

 animal. 



The Guinea-worm (Dracuncuhis or Filaria medinensis) is 

 a Nematode worm, which inhabits, during one stage of its 

 existence, the cellular tissue of the human body, generally 

 attacking the legs, and often attaining a length of several feet. 

 All known specimens of this parasite are impregnated females, 

 containing a large number of young. The worm remains im- 

 bedded in the body, in a more or less quiescent condition, for 

 a year or more, at the end of which time it seeks the surface, 

 in order to get rid of its young. No external aperture to the 

 genital organs has hitherto been proved to exist, and it seems 

 possible that the young are produced within the body of the 

 parent by a process of internal gemmation. The young Filaria 

 consists of a vermiform body, terminating in a hair-like tail ; 

 and when set free from the parent, its further development 

 probably takes place in water, when it is believed to be con- 

 verted into one of the " Tank- worms " so common in India. In 

 this condition it is possible, as some believe, that sexual organs 

 are developed, and that the females are impregnated. The 

 worm is believed to gain access to the body of bathers, when 

 still extremely minute. According to Dr Bastian, however, it 

 appears probable that the Guinea-worm " is a parasite only 

 accidentally, and that it and its parents were originally free 

 Nematoids." 



