2l8 MAINE AGRICULTURAL EXPERIMENT STATION. 1916. 



dulus (36). These are all larvae of the long-tailed, filth-inhab- 

 iting type which live normally in sewage, putrid or stagnant 

 water, in ditches or even in watering troughs (27), and wells 

 (47; 16, p. 5). 



The source of infection in certain cases has been explained 

 as follows : By ingestion of eggs laid on cream, sour milk or 

 cheese; by ingestion of eggs or larvae in drinking water from 

 springs, contaminated by the drainage from compost heaps or 

 from stagnant pools or ditches; by eating water-cress or over- 

 ripe fruit in which larvae may be present ; or by deliberate inges- 

 tion on the part of children. Any of these methods seems p"s- 

 sible and all, except the first and the last, quite probable. 



It is not difficult, as pointed out by Wagner (56), to see how 

 these larvae are able to exist in the alimentary canal, where the 

 conditions would not differ greatly from their normal habitat 

 in faeces. The food is similar, plenty of air is supplied by 

 swallowing, and the mephitic gases are not greatly different. It 

 is not quite clear how the larvae manage to resist passage for 

 many weeks, as certain cases indicate. They have no hooks 

 which would enable them to attach to the intestinal wall unless, 

 indeed, it be the minute ones on the prolegs, which seem inade- 

 quate. 



Austen (2) reports two cases of intestinal myiasis due to the 

 larvae of Syrphus, which are not so easy of explanation ; because 

 what is known of the larval habits of this genus does not indi- 

 cate a ready source of infestation, nor a likelihood that these 

 larvae would readily adapt themselves to the conditions of the 

 alimentary canal. 



The other kinds of myiasis due to Syrphidae are exceedingly 

 rare. Leidy (25) has recorded a case of a rat-tailed larva stated 

 to have been removed from the nasal cavity ; Austen (2) a case 

 of the invasion of the external auditory meatus by a Syrphus 

 larva, resulting in pain and deafness; and Hall and Muir (16) 

 record a case, reported to the Bureau of Animal Industry, U. S. 

 Department of Agriculture, from Maryland in 1909, where eight 

 larvae of Eristalis were stated to have been passed in a jelly-like 

 substance from the vagina of a cow. The source of infestation 

 in such cases as these is doubtless oviposition by the fly directly 

 in these natural cavities of the body; especially if the latter 

 were in a diseased or uncleanly condition. 



