LIFE HISTORY 



289 



Jreed from their cysts and take refuge among the villi and folds 

 of the mucous membrane of the small intestine^ Here they 

 mature^nd copulate as early as the third day after being swal- 

 lowed, _The female worms (Fig. 119) are from three" to four mm. 

 (I to I of an inch) long, whitish in color, slender and tapering 

 from the middle of the body toward the anterior end. The 

 digestive tract of the worm consists of a long muscular pharynx, 

 followed by a simple intestine. The forepart of the intestine has 

 a very characteristic cross-barred ap- 

 pearance. The reproductive system in 

 both sexes is single, i.e., with only one 

 ovary or testis, and occupies a large 

 portion of the body. The arrangement 

 is different in the two sexes, the male 

 reproductive system opening at the 

 posterior end of the body with the anus 

 while the female system opens on the 

 anterior third of the body. The male 

 worms (Fig. 119) are only about half 

 the size of the females. The adult 

 intestinal worms are essentially short- 

 hved, the males usually passing out of 

 the intestine soon after mating, and 

 the females as soon as they have given 

 birth to all of their offspring. The 

 adults usually disappear wit hin two or 

 three months after infection. 



Trichina worms are peculiar in that 



emb. 



trichina 

 spirnli.-i. 



Fig. 119. Adult 

 worms, Trichinella 



they bring forth living young, free of m^ie ($) and female (9); 



" , in ml 1 -1 '^^•> vulva; emb., embryos in 



the eggshell.. They do not nourish oviduct; ov., ovary; t., testis. 

 then- young within the body as do truly ^ ^- ^^fter ciaus, from 

 viviparous animals, but merely retain 



the eggs in the uterus until they hatch. Sometimes the young 

 worms begin to be born within a week after the parents have 

 been swallowed by the host. They are most numerous in the 

 circulating blood between the eighth and 25th day after infection, 

 though the greatest invasion occurs on the ninth and tenth days. 

 When born they are scarcely 0.1 mm, (2H of an inch) in length. 

 The m other worms usually burrow into the walls of the intestine 

 far enough so that the young can be deposited directly into a 



