AIR-BREATHING ENTOZOA. 



15 



lungs (the so-called " tracheae "), and need therefore a direct contact with 

 the air. To understand this properly, we must remember that contact 

 with the air is by no means confined to the outer surface of the body ; 

 many of the internal organs are either continuously or occasionally in 

 communication with the outer air ; and all these organs, in spite of 

 their position in the interior of the body, are occasionally inhabited by 

 air-breathing parasites. 



We often find the larvae of flies within the nose and frontal 

 sinuses of mammals, especially the sheep (Oestrus ovis) ; sometimes, as 

 has been recently reported from Guiana, in man himself (Lucilia 

 hominivora and Sarcopliaga WoMfarti, both belonging to the Musci- 

 dae) ; the larvae of flies (Musca vomitoria, Anthomyia canicularis, Figs. 

 7 and 8) are also sometimes found in the intestine, especially in its 

 interior portion, where air frequently enters along with the food ; in- 

 deed the larvae of G-astrus equi are almost constantly found in the 

 horse in this situation. Other air-breathing parasites live below the 

 skin of mammals (as the larvae of Oestrus and the chigoe), and dwell 

 not in enclosed spaces, but in passages open to the air ; in these cases 

 the apertures of the respiratory organs of the parasite are generally 

 turned towards the exterior, to permit of a free exchange of air. Simi- 

 larly, in parasitic larvae within the body-cavities of insects, the hinder 



FIG. 7. Larva of Anthomyia canicularis 

 from the intestine of man. 



FIG. 8. Larvae of Musca vomitoria. 



portion of the body with its tracheal opening is usually (as in the 

 chigoe) protruded through the outer skin of its host, or is in com- 

 munication with the tracheae of the latter. The occasional presence 

 of dipterous larvae in wounds, abscesses, even in the vagina, and under 

 the praeputium and eyelids, is well known, and is easy to understand, 



