THE HOOKWORMS 69 



near the tip; parasite of the small intestine; life history 

 unknown; pathogenicity probably nil; common in Japan. 

 Three other species of this genus, Trichostrongylus colubri- 

 formis, T. probolurus and T. vitrinus which are common 

 parasites of sheep and other ruminants have been reported 

 incidentally from man. These forms are easily overlooked 

 since the adults are very small and the eggs resemble hook- 

 worm eggs. It is therefore possible that members of this 

 genus are more common in man than is at present reported. 

 Two other species belonging to this family, Haemonchus 

 contortus and Mecistocirrus fordi (Nematodirus gibsoni) 

 which are common parasites of domestic animals, have been 

 reported incidentally from man. 



H. Family Ancylostomidae 



Bursa large with well defined rays; buccal capsule well 

 developed; uteri divergent; parasites of alimentary canal. 



1. Sub-family Ancylostominae. Buccal capsule funnel- 

 shaped, provided on ventral side with hooks or teeth; bursa 

 of male closed all around; only one-third of dorsal ray 

 cleft; course of genital tubes longitudinal. 



Ancylostoma duodenale (Plate VIII, Figs. 2 and 4). Body 

 cylindrical; tapering anteriorly; flesh colored when alive; 

 cuticula ringed; buccal capsule carries ventrally two pairs 

 of hooklike teeth; male, length, about 10 mm.; width 0.4 

 mm. to 0.5 mm.; bursa umbrella shaped; rays shown in 

 figure; two slender spicules, about 2 mm. long without 

 barbs; female 12 mm. to 13 mm. in length; vulva behind 

 middle of body; adults live in small intestine; eggs hatch 

 outside body into rhabditiform larvae; grow in 4 to 6 days 

 into the filariform infective larvae, which enter man through 

 skin or by way of the mouth; frequently produces a serious 

 disease, characterized by intestinal disturbances and anemia; 



