270 



THE ROUND WORMS 



the whip-worm 'the thickened body representing the handle and the 

 narrow neck the lash. It is one of the most common parasites in both 

 temperate and tropical climates. 



The egg is very characteristic in having an oval shape with knobs at either extrem- 

 ity. It resembles a platter with handles. The male is almost 2 inches long, and 

 has the terminal portion curled up in a spiral. It has a single terminal spicule. 



The female is a little longer than the male, and has the terminal part in the shape 

 of a comma instead of being coiled. The neck only contains the oesophagus which 



FIG. 73. Round worms, i, Encysted embryo of Trichinella spiralis; 2, male 

 and female of T. spiralis; 3, male and female of Trichocephalus trichiurus; 4, egg 

 of T. trichiurus; 5 and 6, head and male and female of Ascaris canis; 7, 8, and 9, head, 

 egg and male and female of Oxyuris vermicularis; 10, n and 12, head, egg and tail of 

 Ascaris lumbricoides; 13 and 14, head and egg of Echinorhynchus gigas; 15, 16 and 

 17, parthenogenetic female and rhabditif orm and mariform embryos of Strongyloides 

 stercoralis. 



is contained in a groove in large cells which form a single row like a string of pearls. 

 These cells play a digestion role. The vulva opens at the upper end of the thickened 

 terminal end which contains an intestine lying between the ovary and uterus. 

 The great powers of resistance of the ova may account for their general distribution; 

 they may live for months under conditions of freezing and so forth. There is no 

 intermediate host. The worm arrives at sexual maturity in about one month after 

 ingestion. The whip-worm prefers the caecum, but also lives in the lower end of the 

 ileum and the appendix. 



