The royal natural history . is the free-living male, B represents thefree-living female, and G is the parasiticfemale (w), with her brood-pouch. Of the thread-worms infesting thehuman body, one of the commonest isAscaris lumbricoides, which is found innumbers varying from one or two onlyto over two thousand. These wormsusually infest the small intestine, butsometimes enter the stomach, or evenpenetrate into the liver. Large examplesreach a length of 6 inches or more, andthe females produce about sixty millionsof eggs annually. These are naturallydispersed abroad everywhere, and as theyoung wor
The royal natural history . is the free-living male, B represents thefree-living female, and G is the parasiticfemale (w), with her brood-pouch. Of the thread-worms infesting thehuman body, one of the commonest isAscaris lumbricoides, which is found innumbers varying from one or two onlyto over two thousand. These wormsusually infest the small intestine, butsometimes enter the stomach, or evenpenetrate into the liver. Large examplesreach a length of 6 inches or more, andthe females produce about sixty millionsof eggs annually. These are naturallydispersed abroad everywhere, and as theyoung worm retains its power of growthin spite of frost, drought, and, in fact, themost unfavourable circumstances imagin-able, and is, moreover, far too small to be noticed, we need not feel surprised atthe prevalence of the pest. The form and some of the structural characters ofthis worm are shown in the two illustrations on p. 453. In the uppermost, 1 isthe male, and 2 the female, of the natural size, 3 being the Q^g, enormously. HUMBLE-BEE THREAD-WORM. A, Male enlarged ; a, nat. size. B, Female enlarged : b, nat. size. C, Brood-pouch of female (w) ; c, nat. size. THREAD- WORMS. 453 enlarged; the lower illustration depicting the upper (a) and the lower (6) side ofthe head, with the prominent lips. Other mammals, besides man, are the hosts ofdifferent species of Ascaris. For instance, J., mystax is found in dogs and cats,and sometimes even in man; while A. lumbricoides also occurs in swine. A largespecies, A. megalocephalus, the female of which reaches a length of over a foot, livesin horses and cows. A second common parasite of mankind is Oxyuris vermi-cular is, a small, white, sharp-tailed worm, which measures about one-quarter of
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Keywords: ., bookcentury1800, booksubjectnaturalhistory, booksubjectzoology
