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is the absence of cilia ; this is also characteristic of Arthro- 

 pods. Nematodes move by wriggling ; some are free- 

 living, but most are parasitic during part or the whole of 

 their life, and many of these are important parasites which 

 cause disease in plants, animals and Man. 



Structure and Life-History of Ascaris. 



Where are the Round Worms, Ascaris lumbricoides and 

 Ascaris megalocephala, found ? What is the effect 

 of these Parasites on their Hosts ? 



Ascaris lumbricoides is a frequent parasite of Man in all 

 parts of the world ; it is common also in the pig and other 

 animals, and it lives in the small intestine and stomach. 

 The effect is digestive disorder with toxic symptoms. 



Ascaris. megalocephala is a large species common in the 

 small intestine of the horse. When numerous, the worms 

 cause intestinal obstruction and death may ensue. 



Describe the External Features of Ascaris lumbricoides. 



The triangular mouth has three lips bearing sensory 

 papillae. Four lines, which mark the corresponding ecto- 

 derm thickenings, may be noticed along the body ; the 

 more prominent two are the lateral lines, the other two 

 are dorsal and ventral. On the ventral line, about 2 mm. 

 from the mouth, is the excretory pore ; and about the same 

 distance from the posterior end is the anus (of female) 

 or cloaca (of male). 



The male measures from four to eight inches in length, 

 and about a tenth of an inch in diameter ; the terminal 

 portion of its body is incurved, and two minute genital 

 chaetae or copulatory spicules may be seen projecting from 

 the cloaca. The anal and genital apertures are within 

 the cloaca. 



The female is nearly twice the size of the male. The 

 female genital aperture is situated ventrally in a groove 

 encircling the body about two or three inches from the 

 mouth. 



