244 



INTESTINAL PARASITES. 



FIG. 95. 



female to a blunt tip at the posterior end, while in the male it 

 terminates in a three-lobed bursa. The dorsal lobe has pro- 

 jecting from it two rays, which divide into a bipartite tip. In 

 the Old World worm this tip is tripartite. From the centre 

 of the caudal bursa project the barbed genital spicules, two in 

 number. In the female the vulva is situated ventrally at the 

 junction of the middle and posterior thirds of the body. In 

 copulation the parasites assume a position which resembles the 



shape of the greek letter ^. The 

 females are very prolific, and de- 

 posit their eggs in the intestines. 

 Here they never develop into 

 larvae, but when once excreted 

 the larvae will develop, if oxygen 

 is present freely, in about twenty - 

 four hours. If then they have 

 access to a proper environment 

 a loose sandy soil is most propi- 

 tious for them they will proceed 

 to develop. A moulting takes 

 place, after which the larvae be- 

 come encysted. This is the stage 

 at which they are infectious to 

 man. They may be ingested di- 

 rectly with the food or water, and 

 thus reach the stomach. They 



Four eggs of the New World hook- , . , , -, , i v 



worm, in the i-, 2-, and 4-ceii stages, may also enter the body through 



the skin, causing a severe derma- 



tfents, and give a positive diagho- titis (ground J teh )- Hence, they 



sis of infection. Greatly enlarged, are carried by the circulating 



blood, and find lodgment in the 



lungs, whence they escape up the trachea and are swallowed. 

 When the ova reach the stomach by either route, the encysted 

 capsule is softened by the stomach juices, and the larva devel- 

 ops into an adult worm and passes to the duodenum, where 

 the conditions seem more favorable to their development. 

 Here the males and females cohabitate, the ova are passed 

 out, and the cycle of worm-life goes on. In the intestine 



