202 PARASITES IN THE INTESTINES 



mammary glands and are swallowed by the young while 

 nursing. Birds are less commonly affected with round worms, 

 and as a rule they harbor only a few specimens. Occasionally, 

 however, round worms are found in birds in large numbers, 

 especially in certain localities where this form of parasitism 

 may be enzootic. Pigeons are the common victims; in some 

 cases whole flocks succumb to the infestation. 



Round Worms in the Intestine of the Dog.— Belascaris 

 marginata.— This species is similar to the B. mystax of the 

 cat, and is somewhat larger. The body is white or reddish, 

 head usually curved and provided with two membranous 

 lateral wings, which cause it to look like an arrow head. 

 Male 5 to 10 cm. long, tail curved. Female slightly longer, 

 tail obtuse. Ova almost globular and 75 to 80 microns in 

 diameter. Capsule thick and showing circular striations; 

 granular center with small clear space between it and the 

 capsule 



Toxascaris limbata (T. marginata) .— This parasite is simi- 

 lar to the above; found in intestinal tract of dogs; rare in 

 United States. 



Echinorhynchus cants. —Occasionally found in the dog in 

 certain districts (Texas) . 



Round Worms in the Intestine of the Cat.— Belascaris 

 mystax.— This round worm is slightly smaller than the B. 

 marginata of the dog, the male being 4 to 6 cm., the female 

 4 to 10 cm. long. Ova slightly smaller than B. marginata, 

 60 to 75 microns in diameter. Similar to B. marginata only 

 smaller. 



Round Worms in the Intestine of the Rabbit.— Oxyuris 

 ambigua (Passolurus ambigus),— This is a white fusiform 

 worm, male 3 to 5 mm. long, female 8 to 11 mm. The body 

 of both sexes terminates in a suddenly tapering tail, 0.22 mm. 

 in length. It infests the large intestine and cecum. It is not 

 so common as the round worm of the dog and cat, nor does 

 it occur in as large numbers. Ova globular and very small, 

 with thick capsule similar to B. marginata. 



Round Worms in the Intestine of Birds.— Heterakidoe.— 

 (a) Heterakis papillosa (Heterakis vesicularis).— This is a 

 common species infesting chickens, and occasionally ducks. 



