520 



EVOLUTION OF ANIMALS 



Part V 



Fig. 26.1. A free-living nematode worm. Vinegar eels (Tiirbatrix aceti) cul- 

 tured on an agar (gelatin) plate. They are minute, little longer than the width of 

 a pinhead. They flourish on the fungus that abounds in the "mother" of raw 

 cider vinegar; they also live in sour paste. (Courtesy, General Biological Supply 

 House, Chicago.) 



Ascaris usually spreads from man to man with no other animal implicated. 

 Ordinarily eggs from the Ascaris of pigs do not develop in man nor those 

 from the Ascaris of man in pigs. However parasites may be otherwise re- 

 garded, they deserve respect for their sensitive discrimination of environ- 

 ments. 



Life History of Ascaris lumbricoides. The adults live in the small in- 

 testine where they feed mainly upon the partly digested food of the host, also 

 upon blood from the intestinal walls. The mature worms mate and each female 

 produces over 20 millions of eggs. These are freed in the intestine and as 

 embryos within the thick, resistant egg shells they pass out of it with the 



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 ventro-/atera/ //p 



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Fig. 26.2. Ascaris lumbricoides, a human parasite probably introduced to man- 

 kind when pigs were first domesticated. Upper, outline of the body of the female. 

 Lower, the sucking mouth guarded by three lips by which it can grasp and suck 

 blood from the lining of the intestine although it feeds more regularly on the 

 digesting food. Length of adult females, 8 to 14 inches; males, 3 to 5 inches. 

 (Courtesy, Curtis & Guthrie: General Zoology, ed. 4. New York, John Wiley and 

 Sons, 1947.) 



