256 PARASITES OF THE DOMESTIC ANIMALS 



intestinal infestation. Again, the general rule applies that resistance is 

 always reduced in animals in low physical condition, while, essentially, 

 crowding and general unsanitary conditions favor the transmission and 

 spread of the parasites. 



Of the Strongylidae three subfamilies may be distinguished, viz: 



Subfamily I. Metastrongylince. 



Subfamily II. Trichostrongylinae. 



Subfamily III. Strongylinae. 



Subfamily I. Metastrongylix^ 



Strongy-lidse (p. 255). — This subgroup comprises the strongyles 

 parasitic in the respiratory system and some in the circulatory system. 

 The buccal capsule is absent or very slightly developed. The bursa of 

 the male is frequently atypical in structure and number of rays. There 

 are two equal spicules. The eggs are in varying stages of development 

 when deposited. 



The life history is as yet unknown. It is probable that infection is 

 without intermediate host. Romanovitch and Slavine (1914) found 

 that eggs of Didyocaulus filaria when placed in water formed embryos. 

 Two moltings followed, the cuticle being retained and encapsulating the 

 larvae, and these when fed to sheep produced infection with the adult 

 worms. This would indicate direct development and infection by the 

 worms of this group. 



Bronchial and Pulmonary Strongylosis of the Sheep and Goat 



Three species of Metastrongylinse invade the respiratory tract of the 

 sheep and goat; a fourth, — Metastrongylus apri — described under 

 broncho-pneumonia of the hog, is exceptionally found in the sheep. 



1. Dictyocaulus filaria (Strongylus filaria). Fig. 130. Meta- 

 strongylina? (p. 256). — The body is white, filiform, slightly tapering at 

 posterior extremity. The anterior extremity is obtuse, without wings; 

 mouth circular and without papillae. The bursa of the male is notched 

 in front; spicules short, thick, brown in color, and provided with mem- 

 branous wings. The caudal extremity of the female is straight and 

 conical; vulva somewhat posterior to the middle of the body. 



Length of female, 5-10 cm. (2-4 inches); male, 3-8 cm. (1 1/8-3 1/8 

 inches). 



The eggs are oval, 112-135 microns in length by 52-67 microns in 

 breadth. They contain developed embryos which are liberated in the 

 bronchi as the eggs are deposited. 



The embryos are 540 microns long ]:)y 20 microns in diameter, tapering 

 to a blunt point behind. 



