HOOK WORMS. 



217 



being bipartite in the division of dorsal ray rather than tripartite, as 

 with the A. duodenale. 



The delicate-shelled eggs pass out in the faeces and in i or 2 days a 

 rhabditiform embryo (200 x 14/4) is produced. After moulting twice, 

 it remains rather quiescent; it is at this stage that it burrows into the 

 skin of man, producing the so-called " ground itch" at the site of 



7. 



FIG. 68. Hookworm anatomy, i, Rhabditiform embryo of Strongyloides ster- 

 coralis emerging from egg; 2 and 3, egg and male and female of hookworm; 

 4 and 5, head and copulatory bursa of male Ancylostoma duodenale; 6 and 7, 

 head and copulatory bursa of male Necator americanus. Dorsal ray, N, america- 

 nus. shows deep cleavage and bipartite tips. 



entrance. Having gained access to the lymphatics and veins, they 

 eventually reach the lungs. Here they get into the bronchioles and 

 undergo a third moulting. They then w r ork their way up the trachea 

 to the glottis and are swallowed to then become adults in the intestine. 

 Dr. Stiles, \vhile accepting this theory of the life history, thinks it 

 15 



