248 PARASITES OF THE DOMESTIC ANIMALS 



Experiments by Ransom and Hall have shown that dung beetles and 

 croton bugs fed upon the eggs of Gongylonema scutata become infested 

 with an encysted larval stage of the parasite. Evidence is thus furnished 

 that the mammalian hosts of the worm become infested as a result of 

 swallowing insects bearing the encysted larvse. 



2. Filaria labiato-papillosa (F. cervina). Filariidse (p. 244). — This 

 species resembles Setaria labiato-papillosa of the horse, but differs from 

 it in the absence of transverse striations of the integument and in the 

 caudal papillae of the female, which form a terminal cluster of small 

 blunt points, anterior to which are two thick conical papillae. 



Length of female, 6-12 cm. (2 3/8-4 3/4 inches) ; male, 4-6 cm. 

 (1 1/2-2 3/8 inches). 



Development and hatching is within the body of the female (ovovi- 

 viparous) . The freed embryos are 140-230 microns in length. 



This nematode of the ox and deer is found almost exclusively in the 

 peritoneal cavity. It does not appear to have any effect upon the health 

 of its hosts. A worm occasionally found in the eye of the ox is con- 

 sidered as belonging with this species. 



FiLAEIIDiE OF THE DoG 



1. Dirofilaria immitis (Filaria immitis). Fig. 129. Filariidae 

 (p. 244). — The body is white, long, decidedly thread-like, with ends 

 having an obtuse appearance. The mouth is small and surrounded by 

 six indistinct papillae. The posterior extremity of the male is slender, 

 rolled spirally, and bears two small lateral wings. There are two 

 spicules. The posterior extremity of the female is obtuse. 



The female is 25 to 30 cm. in length and about 1 mm. in diameter 

 (9 3/4 inches by 1/32 of an inch). The length of the male is 12-18 cm. 

 (4 3/4-7 inches). \ 



The embryos are developed and hatched in the body of the female 

 (ovoviviparous). As they enter the circulation they measure 285- 

 295 microns in length and have a diameter of about 5 microns. The 

 anterior extremity is obtuse, the posterior extremity attenuated and 

 slender. 



Occurrence. — Hematic filariasis of dogs, produced by this species^ 

 has been most frequently met with in China and Japan, about fifty 

 per cent, of all dogs in the latter country, it is estimated, being affected. 

 It occurs also in other countries, including North America. 



The usual seat of invasion is the blood-vascular system, particularly 

 the right ventricle of the heart, the pulmonary arteries being more 

 rarely involved. Not infrequently mature filariae are found in the sub- 

 cutaneous connective tissue. In the heart and large arteries the worms 

 may be found in a tangled mass containing hundreds so interlaced as tO' 

 make it difficult to extricate single individuals. 



