2l8 THE ROUND WORMS. 



probable that infection is also brought about by swallowing directly some 

 infecting stage. 



Necator americanus. This is the species of hook-worm found in 

 the Southern States and the West Indies. It is very prevalent in Guam, 

 L. I. It was found by Looss in pigmies from Central Africa, so that 

 this parasite was undoubtedly brought to this part of the world by 

 slaves. The eggs of N. americanus are larger than those of A. duode- 

 nale. In hook-worm disease we have ground itch, tibial ulcer, anaemia, 

 interference with physical and mental development and, in bad cases, 

 dirt eating. 



ASCARID^:. 



These have 3 papillae around oral cavity. The male has 2 equal- 

 length spicules. An intermediary host is not needed in the life history 

 of this family. 



Ascaris lumbricoides. The male worm is from 5 to 8 inches 

 long and the female from 7 to 15 inches in length. They are from 1/7 

 to 1/4 of an inch in diameter. The body of the worm resembles the 

 ordinary earth-worm, but is more grayish than red. The ova are very 

 characteristic with a rough mammillated exterior. This at times is 

 shelled off and we have a smooth egg which may be mistaken for eggs 

 of other parasites. The eggs leave the body in the faeces and after a 

 long time a few weeks to several months, according to temperature- 

 develop an embryo which remains in the shell until swallowed by some 

 man or animal. It is stated that they will remain alive for years. On 

 being swallowed, the embryo leaves the egg and we have males and 

 females developing in the intestine. In countries where such parasites 

 abound, as in Guam and the Philippines, the possibility of their getting 

 into the peritoneal cavity through operative measures on the intestine 

 must always be thought of. 



Ascaris canis. This is a parasite of the dog and cat, but is oc- 

 casionally found in children. It is much smaller than the A. lum- 

 bricoides male is 2 to 3 inches long, female 4 to 5 inches in length. 

 The parasites are characterized by the presence of wing-like pro- 

 jections from the anterior end (arrow-like head). 



Oxyuris vermicularis. This parasite is also known as the pin- 



