300 



General Biology 



(Fig. 187), of the family Trichinellidae, which causes a very dangerous 

 disease called trichinosis in rats, pigs, and man. 



The female Ascaris is the larger of the sexes; in fact, it may grow 

 to a length of from five to eleven inches and a quarter of an inch in 

 diameter. The body is of a light brown color, with a narrow white 

 stripe along the dorsal and ventral surface, and a broader white line 



Fig. 186. Tuberculous Cavity in Oesophageal 

 Wall of Man Containing an Ascaris 

 Lumbricoides. (From a photo- 

 graph lent the author by 

 Dr. E. L. Miloslavich.) 



Fig. 187. Trichinella Spiralis. 



A. Encysted Trichina Embryo. 



B. Adult female from Intestinal wall. 1, 

 parasite; 2, membrane of cyst; 3, muscle-fiber 

 of pig. (After Leuckart.) 



lying on each side of the dorsal and ventral stripe. 



The mouth-opening (which is surrounded by one dorsal and two 

 ventral lips) lies at the anterior end of the animal. The anal opening 

 lies at the posterior end. The tail-end of the female is straight, while 

 in the male it is slightly bent. In the male also there are penial setae, 

 which extend through the anal opening and which are used for copu- 

 lation. 



The Digestive System. 



The digestive system is very simple, consisting of a mere straight 

 tube into which the already digested food of the host enters. A definite 

 coelom may also be seen. The more anterior portion of the digestive 

 tube is known as the pharynx. This is muscular, so that by contraction 



