114 



is at present known about the possible development of these 

 species in other flies, and as it would appear that the usual 

 mode of development is ae outlined above, the possible 

 association of Musca domestica and Stomoxys calcitrans with 

 the production of the lesions must be considered. 



The affection, as it has been observed by the present 

 writer and by Lewis and Seddon, is most commonly situated 

 in or about mucous membranes, viz., the mucous membrane 

 of the urethra and that of the eye. Lesions are found, 

 nevertheless, in other situations as on the sheath or the limbs. 



Why should these lesions be more commonly found in 

 mucous membranes? The first explanation which suggests 

 itself is that Musca domestica is attracted to these situations 

 in search of moisture and food. Should larvae escape from the 

 proboscis during feeding operations, there would be sufficient 

 moisture present on the mucous membrane to prevent desicca- 

 tion. Under these conditions it is possible for the larvae 

 to penetrate the mucous membrane should they desire to and 

 be capable of so doing. 



Larvae found in the lesions resemble those of Habronema 

 muscae and H. megastoma, the cuticle of both these forms 

 possessing longitudinal ridges, but not those of H. microstoma, 

 the cuticle of this form showing no longitudinal ridges. 



H. megastoma is found in tumours situated in the sub- 

 mucosa of the stomach of the horse. It is generally believed 

 that it perforates the gastric mucous membrane, probably 

 when in the larval stage. In its normal situation the parasite 

 would live on the products of the tissues rather than on the 

 semi-digested material in the alimentary canal. It is, there- 

 fore, a parasite of tissues rather than of the contents of the 

 alimentary canal. 



From a theoretical consideration one would expect the 

 larva of H. megastoma to possess the instinctive desire to 

 penetrate mucous membranes, and, further, to be able to 

 maintain its life in the submucous tissues of the urethra and 

 conjunctiva or the subcutaneous tissues longer than the larvae 

 of the other two species. This suggests that the larva of 

 H. megastoma is more likely to produce a habronemic granu- 

 loma than the larvae of the other two species. Experimental 

 evidence also suggests that the larva of H. megastoma more 

 'readily penetrates the conjunctiva of the horse and sets up 

 a granulomatous reaction, and also that it more readily sets 

 up a granulomatous condition in the subcutaneous tissues than 

 the larvae of H. muscae. 



Although the experimental evidence suggests that the 

 larva of II. muscae does not readily penetrate the conjunctiva 

 or produce a granulomatous reaction in the subcutaneous 



