THE ANIMAL KINGDOM 



407 



Necator americanus, the American hookworm, is found in the 

 intestine of man and the gorilla, where it lives on the blood of its 

 host, after first making a wound with its cutting lips and teeth. 

 The adult male is 9 mm. in length, and the female 11 mm. 

 After copulation, the female deposits numerous eggs, which do 

 not complete development until discharged with the feces. 

 Development then proceeds, the embryo molting twice and 

 remaining inside of the loosened skin after the second molt. 

 There are two general modes of infection: (1) through the mouth, 

 in which case the larva passes directly to the intestine; (2) 



Fig. 234. Fig. 235. 



Fig. 234. — Trichinella spiralis, encysted in the muscle of the pig. (After 

 Leuckart.) 



Fig. 235. — Enlarged view of the dorsal side of the anterior end of the hook- 

 worm Necator americanus, showing the quadrangular shaped mouth opening 

 through which two of the flat, platelike teeth can be seen. (After Stiles.) 



through the skin of the feet and hands, from which it is carried 

 by the blood to the lungs. Considerable damage is then caused 

 by the animal boring through the lungs, heart, trachea, etc., 

 to the intestine (Fig. 235). 



The hookworm is a serious menace in the South, especially in 

 localities where precautions are not taken to avoid soil and 

 water pollution. 



Ascaris lumbricoides is an intestinal parasite, especially com- 

 mon in children. The male averages about 20 mm. in length by 

 3 mm. in diameter, and the female 30 by 5 mm. The eggs pass 

 out with the feces and develop directly to the larval stages in 

 water or moist soil. Infection is by mouth from water, soil, and 

 the skin of raw fruits (Fig. 236). The larvae bore through the 

 walls of the intestine of the host, migrate through the lungs, 

 liver, or heart, and then return to the intestine where they 

 complete their development. 



