Geographical distribution.—So far as determined, the distribution of N. americanus includes in America—Virginia, North and South Carolina, Georgia, Florida, Alabama, Texas, Porto Rico, Cuba, and Brazil. It has been found by Looss in pygmies from Central Africa, and by others in India (Assam, Burma, Ceylon), West Africa, Rhodesia, Fiji, the Philippines, and elsewhere. Probably it is as widely diffused as A. duodenale; and in certain localities, Fjii and Ceylon for example, it is the commonest form of ankylostomum encountered.
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| Fig. 182.—Necator americanus. a, Bursa; b, head. |
Fig. 183.—Necator americanus, head. |
| (After Looss.) | |
The parasite (Figs. 181-3).—N. americanus can be readily distinguished from Ankylostomum duodenale; it is a shorter and more slender worm. The male measures from 7 to 9 mm. in length by 0·3 to 0·35 mm. in diameter; the female, 9 to 11 mm. in length by 0·4 to 0·45 mm. in breadth. The buccal capsule is much smaller, and presents an irregular border; instead of four ventral hook-like teeth, it has a ventral pair of prominent semilunar plates similar to those of the dog hook-worm, Uncinaria stenocephala; the pair of dorsal teeth is likewise represented by a pair of slightly developed chitinous plates of the same nature. The outlet of the dorsal head-gland, usually called dorsal rib or dorsal tooth, projects prominently in the oral cavity. Deep in the
