AIR-BREATHING ENTOZOA. 



15 



lungs (the so-called " tracheEe "), 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 avis) ; sometimes, as 

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

 hominivora and Sarcophaga Wohlfarti, both belonging to the Musci- 

 dse) ; the larvae of flies (Musca vomitoria, Anthomyia canindaris, 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 Gastrus 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. 



Fio. 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 trachea of the latter. The occasional presence 

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

 the prffiputium and eyeM§l%%ell kno^^ffil is easy to understand. 



