ASCARIS 273 



Ascaris or Eelworm. — Of greatest importance of these lesser 

 intestinal parasites is the eelworm, Ascaris lumbricoides (Fig. 

 106). Ascaris is one of the largest nematode parasites known, 

 the female averaging about ten inches in length, and occasion- 

 ally measuring a foot and a half, while in diameter the body is 

 about as large as an ordinary lead pencil. The males are usually 

 several inches shorter. These worms are among the most fre- 

 quent human parasites. They occur in all parts of the world 

 and are found, especially in children, in the majority of temperate 

 countries, even in countries as far north as Greenland and Fin- 

 land. In the tropics they are abundant and are almost univer- 

 sally present in children, each individual harboring anywhere 

 from two or three to several hundred worms. 



Ascaris can be recognized immediately by its large size and 

 robust form. The males (Fig. 107) can be distinguished by the 



Fig. 107. Ascaris, dissected to show anatomy; female above, male below. 

 Note ribbon-like intestine (cross-barred) with pharynx at its anterior end; the 

 coiled threadlike ovaries in female and testis in male; the large kinky oviducts in 

 the female, uniting to form a vagina near the external opening on the anterior third 

 of the body; and in the male the large sperm duct opening at the ventrally-ourved 

 posterior end of the body in common with the intestine. 



sharp downward curve of the posterior end of the body, the female 

 (Fig. 107) having a straight and rather stumpy tail. Both 

 sexes are more slender at the head than at the tail end. The 

 sexual organs occupy the greater part of the body. In the female 

 theyconsist of two coiled threadhke ovaries (Fig. 107) and a pair 

 of large oviducts in the form of kinky tubes which open about 

 one-third of the way back from the anterior end. In the male 

 there is a single coiled threadlike testis and a single sperm duct 

 (Fig. 107), the latter opening at a cloaca at the posterior end of 

 the body. The size and simphcity of the organs makes Ascaris 

 a favorite subject for class-room dissection. The human species, 



