138 



ANIMAL PARASITES. 



posterior end. The intestine is straight. The sexes are in most forms 

 distinct, the male being in general smaller than the female. 



Ascaris lumbricoides. This is one of the most common of the human 

 intestinal parasites, and is of particularly frequent occurrence in chil- 



FIG. 64.- EGGS OF NEMATODE WORMS. 



A, Eggs of Ascaris lumbricoides, X about 300. B, eggs 

 of Oxyuris vennicularis, X about 250. 



FIG. 63. ASCARIS LCMBRICOIDES. About half natural size. 

 A, Male. B, Female. After Perls. 



dren. It is of a light -brownish or reddish color. The female is from 30 

 to 40 cm. long and from 5 to 6 mm. thick. The male is somewhat more 

 than half as large (Fig. 63). Both sexes are pointed at the ends, the 

 posterior end of the male being 

 curved into a spined hook. The 

 eggs, from 0.05 to 0.06 mm. in 

 diameter, are surrounded by an 

 albuminous envelope (Fig. 64^4) 

 and are quite resistant to destruc- 

 tive agencies. The mode of de- 

 velopment and life history of these 

 parasites are not very well under- 

 stood. Their usual seat in man is 

 the small intestine, but they may 

 wander into the stomach, and ex- 

 ceptionally get into the mouth, 

 nose, bronchi, gall passages, peritoneal cavity, etc. They may be single 

 in the gut or present in great numbers. 



Two other species of ascaris have been found in man. A. maritima 

 was found in the vomit of a child in Greenland, in an 

 immature condition. A. mystax, a tolerably common 

 form in cats and dogs, has been found a few times in 

 man. It is smaller than A. lumbricoides. 



Oxyuris vermicularis (Threadworm or Pin worm). 

 This species is very small ; the female has a pointed tail 

 and is about 1 cm. long. The posterior end of the male, 

 which is about 4 mm. long, is blunt, and after death 

 somewhat curled (Fig. 65). The eggs (Fig. 64 B} are 

 produced in great numbers, are oval, and about 0.052 

 mm. long. This parasite is very common in children, 

 and may be present in large numbers in the colon. 

 This worm is known to infest only the human subject, and infection 

 doubtless occurs by the ingestion of the eggs, which are widely dis- 

 tributed in a variety of ways on many objects, fruits, etc. 



FIG. 65. OXYI-RIS 



VERMICULARIS. 

 A, Female. B, Male. 



