Etiology. 



453 



From the oblong ova (Fig. 51), opening by a lid and glued 

 to the hairs in a downward direction, there issne, after a few 

 days, slender larvae composed of 

 thirteen segments. The horses lick 

 these larvie, probably because of 

 itching, get them into their months 

 and ingest them with the food and 

 water into the stomach; here the 

 larvje bore into the mucosa and de- 

 velop. According to another view, 

 the larv« wander in the mouth from 

 various portions of the body of the 

 horse, or to a place where they can 

 be licked off. After about ten 

 months, that is, between May and 

 September, especially, however, in 

 July, they become detached from 

 the mucosa and get into the out- 

 side world with the contents of the 

 stomach or intestines. They change 

 into the chrysalis stage, either in 

 the ground or in horse manure. The 

 flies creep out after thirty or forty 

 days and after copulation the fe- 

 males deposit their ova on horses. 



Fig. 51. Ovum with larvae of Gas- 



troi)liilus equi. Figures to the right 



double magnification, to the left 



highly magnified. 



The body of the bot-fly larvfe is oblong, pointed in front, rounded 

 off behind ; it is composed of eleven rings more strongly curved on the 

 dorsal aspect; the anterior rings are supplied with fine spikes at their 

 dorsal margin. The first segment is supplied with two chitinous mouth- 

 hooks, and above them two buttonlike antennae or feelers. The full- 

 grouTi larvae are up to 20 mm. long and reddish to yellowish-gray in 

 color. 



The larva of the following species of Gastrophilus occur in the 

 stomach of the horse : 



1. Gastrophilus equi (large ntoniaeh Ijot-fly) : A fiy twelve to fourteen 

 mm. long which lays its eggs preferably on the anterior portion of the body of the 

 horse. The larvae adhere to the esophageal portion of the stomach. This fly is very 

 widely disseminated and most larvae occurring in the stomach of the horse belong to 

 this species. 



2. Gastrophilus haemorrhoidalis (rectum bot-fly) : Somewhat smaller, dark 

 brown, likewise widespread bot-fly; the females deposit their ova preferably on 

 tlie lips on the tactile hair of the horse, also frequently on other parts of the an- 

 terior portion of the body. The larviB are somewhat smaller, dark-red and they are 

 parasitic on the pyloric portion of the stomach of the horses, also in the duodenum; 

 after they are fully developed and shed, they remain for some time in the rectum, 

 where they assume a green color, after which they are voided. 



3. Gastrophilus pecorum (cattle bot-fly) : Twelve to fifteen mm. long, 

 dark brown. The larvae are particularly common in Hungarian and Eussian horses; 

 they are thirteen to fourteen mm. long, of a dark brown color, are preferably found 

 in the stomach and duodenum and, after full development, remain in the rectum for 

 some time. 



4. Gastrophilus nasalis (nose bot-fly) : Light chestnut l)rown, twelve to 

 thirteen mm. long, more rare than the preceding species. The yellowish-white larvae 



