180 SURVEY OF J]\ VERTEBRATES 



skin open. Its posterior end on which the hirge stigmata 

 are located, alternately retracts and protrudes through 

 the opening. Thus there is no doubt that this animal 

 can get as much oxygen as it wants. The situation is 

 probably different in immune or partly immune hosts, 

 since here a scab occludes the opening and presumably 

 interferes with the normal oxygen supply of the parasite. 

 The latter survives nevertheless. 



Experimentally, it has been shown that at least the 

 third instar larva of Cordylohia is quite resistant to 

 lack of oxygen. It survived in nitrogen for 27 hours 

 and — what is especially remarkable in view of the diifer- 

 ent behavior of the majority of other insects — it remain- 

 ed motile for 22 hours. The first instar larva is more 

 sensitive; it survived more than 2M2 hours but less than 

 19 hours. Pupation was also found to be possible in the 

 absence of oxygen. A larva that had been kept in ni- 

 trogen for 48 hours and had pupated during this time 

 developed into a normal fly upon readmission of air. An- 

 other pupa, however, did not survive a 3-day period 

 without oxygen. 



Non-parasitic aithropods are occasionally found in 

 parasitic habitats in which they must presumably lead 

 a more or less anaerobic life. The best-known instances 

 are those encountered in the so-called urinary and intes- 

 tinal myiasis. Numerous cases have been described in 

 which arthropods (acarines, myriapods, larvae of coleop- 

 tera and especially diptera) weve recovered from human 

 urine or feces. It has been claimed that the animals had 

 passed through the alimentary canal alive, or even that 

 they had become established for long periods in the 

 stomach, the intestine or the urinary bladder. 



It is obvious that the possibilities of error in such cases 

 are many. Hysterical patients may be too imaginative 

 or the receptacles that they used may not be clean. Chev- 

 rel (1908) who reviewed the cases of urinary myiasis 



