LIFE-HISTORIES 



143 



stomata of a young wheat plant, or pierce the cell-wall with a 

 projection from the buccal lining, and crawl up through the 

 tissues to the flowers, where the life-cycle begins again. 



Heterodera by contrast is an ectoparasite. The female larva 

 attaches herself to a root of tomato, 

 cucumber, beet, or other plant, 

 and sucks the sap. She is fertilised 

 by visiting males. 



3. Free as larvcs, parasitic in 

 animals as adults. — Ascaris is one 

 example of this type ; another is 

 Ancylostoma duodenale, the hook- 

 worm (Fig. 106), which is pink, 

 and lives in the small intestine 

 of man. The male is 8-1 1 mm. long, 

 the female 10-18 mm. It browses 



on the tissues, and so causes a considerable anaemia. Copulation 

 occurs, and the eggs are laid and are passed to the exterior 

 having divided to the four- or eight-cell stage. Further develop- 

 ment requires air, moisture, a moderately high temperature. 



Fig. 105. — The Corn-cockle ^^'o^m. 

 From Theobald. 



A, Cockle gall ; C, larvae ; D, gaU cut open ; 

 E, larvae magnified. 



Fig. 106. — The Hookworm {Ancylostoma duodenale). — Fromi Parker and 



Has well, after Leuckart. 



A, Male and female in coitu ; B, anterior end ; C , mouth, with spines ; D, hinder end of male, with e.xpansion 



known as bursa ; cv.gl., cervical glands ; ph., pharynx. 



and preferably darkness. In temperate climates they can there- 

 fore only grow in such places as mines and tunnels, which has 

 led to the animal being known in this country as the miners' 

 worm, and the disease which it causes as miners' anaemia. In 

 all tropical and sub-tropical countries, however, the worm is 

 widespread, as the larvae can develop in the open. The third- 

 stage larva, which as is usual in nematodes is the infective or 



