SURVEY OF INVERTEBRATES 131 



reported iu the medical literature considers 7 of them as 

 genuine. Newer trustworthy cases were later reported by 

 King (1914) and Leon (1921). Intestinal myiasis was re- 

 view^ed by Seifert (1926) and Herms (1939); some new 

 instances have been described by Chagnon (1940), 

 Swartzwelder and Call (1942) and Chandler (1943). A 

 survey of the literature seems to indicate that at least 

 a number of the cases reported are not a result of imagi- 

 nation or faulty observation. 



The question then naturally arises as to how the 

 myiasis-producing animals can resist the variety of ad- 

 verse conditions that they encounter, for example, in the 

 intestinal tract. Experimental studies, such as those of 

 Desoil and Delhaye (1922), Hoeppli and Watt (1933), 

 Komarek (1936) and Causey (1938) are not too enlight- 

 ening in so far as the explanation of myiasis is concerned. 

 In no case w^as it possible to establish insect larvae within 

 experimental animals; as a matter of fact, such larvae 

 always died rather rapidly. The evidence concerning the 

 point of primary interest in this discussion, namely, how 

 the animals survive at the low oxygen tensions jDrevail- 

 ing in the intestine, is also rather negative. Komarek 's 

 experiments certainly fail to indicate a sufficient resis- 

 tance of dipterous larvae to oxygen lack. It is regret- 

 table that no one has tried to rear under low oxygen ten- 

 sions insect larvae recovered from myiasis cases. Could 

 it not be possible that in the genuine myiasis cases the 

 animals belonged to strains (or were mutants) especially 

 resistant to oxygen deficiencies! There is certainly no 

 valid ground to assume that a normal dipterous larva 

 should be able to live for w^eeks or even months at those 

 oxygen tensions that usually prevail in the intestine of 

 vertebrates. 



