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diameter remaining approximately constant throughout. The 

 presence of an open anus at the base of the tail is against its 

 being a Habronema larva. A larval Habronema has a closed 

 anus with a very prominent anal operculum in the early stages, 

 and only in the final larval stage is the anus open. It seems 

 possible that the form may be an aberrant larva of H. 

 microstoma, as is sometimes seen in Musca domestica. It is 

 also possible that the larva does not belong to the 

 genus Habronema. Railliet has taken the presence of this 

 larva in one sore examined by Descazeaux as evidence in favour 

 of his theory that embryos of Habronema are capable of 

 developing through their larval stages in the skin of the horse. 

 If the form is a larval Habronema it is certainly aberrant, 

 but there is no proof that it has developed from an embryo in 

 the skin of the horse. There is no proof, moreover, that the 

 form is a larval Habronema. It is doubtful, then, that this 

 finding really can be taken as supporting Railliet's theory. 



Further, there is little support for Railliet's theory to be 

 found in the fact that Fayet and Moreau did not describe 

 the presence of a spinous tip to the tail of the larva they found. 

 In all other respects their larva resembles that usually found 

 in "summer sores," and it is probable that they failed in 

 common with others to detect the spinous tip. 



The fact that larvae at an earlier stage than the final 

 are sometimes present in the proboscis of a fly must not be 

 overlooked. Should these earlier larvae be present in the 

 proboscis along with larvae in the final stage, and 

 should the larvae escape from the proboscis, it is possible that 

 these earlier larval stages may be present in a lesion along with 

 the later stages. Therefore, the finding of larvae of an earlier 

 stage could not be taken as proof of development of the larvae 

 in the tissues of the horse. 



Van Saceghem's observations and experiments strongly 

 suggest that flies play an important role in the production of 

 the lesions. His experiments have shown that the larvae of 

 Habronema when placed in the inner canthus of the eye are 

 capable of setting up a typical habronemic conjunctivitis. He 

 showed, further, that an open . wound may develop into a 

 typical "summer sore" if the animal is placed in an environ- 

 ment where flies are heavily infested with larvae. This is 

 strong presumptive evidence in support of his conclusion that 

 the larvae in the wound escaped from the proboscis of the fly 

 when the latter came to feed upon the raw surface. 



Larvae found by him in "summer sores" were 50 ja in 

 diameter, and showed marked longitudinal striations in the 

 cuticle, whereas those found in flies caught in a stable were 

 65 /x in diameter and showed no longitudinal striations. He 



F 



