98 S. HADWEN AND A. E. CAMERON. 



egg. The length of time that moisture is applied may also'determine the rate of 

 hatching.* 



From the foregoing table it would appear that the eggs of G. nasalis hatch most 

 readily of the three species without artificial aid (51 per cent.), a fact which is more 

 than interesting in view of the position where the eggs are deposited on the host, 

 namely, the intermaxillary region. This also agrees with our theory that the larvae 

 of G. nasalis may penetrate the integument of the host directly, since it is manifestly 

 impossible that the animal could reach the eggs with its hps or tongue. 



Actually, 51 is a low estimate of the percentage of hatching of G. nasalis eggs, 

 for it does not take into account the fact that in the case of the batch of 79 eggs 

 several had hatched before being collected. 



It would be unwise to generalise from the results obtained in the case of the eggs 

 of G. haemorrhoidalis, owing to the small number with which we dealt. 



In passing, it may be observed that the eggs of G. intestinalis are disposed on the 

 hairs differently from those of G. nasalis. On long hairs bearing a number, the 

 eggs of the former are usually separated from each other more widely than are those 

 of the latter, of which as many as 7 and 8 eggs are often deposited in close series, 

 the anterior extremity of one in contact with the posterior extremity of its immediate 

 neighbour. As already remarked, the eggs of G. haemorrhoidalis do not have the 

 stalk touching the skin of the host, and generally there is but one egg on each hair. 



Do the recently emerged Larvae of Bot-flies penetrate the Integument of 



the Host? 



It is significant to note that about the time that the larvae of G. nasalis were 

 hatching from the eggs in maximum numbers, numerous small scabby areas were 

 observed in the intermaxillary region of the host. As to whether the cause could 

 be attributed to the animal rubbing the affected part on fence-posts, is a moot point. 

 In the animals examined, it could not be shown that the hair under the jaws had 

 been rubbed off, as one would have naturally expected had the above been the reason. 

 It is just possible that the newly-hatched larvae were the direct agents concerned 

 in producing this abraded condition of the skin. Although we cannot substantiate 

 this theory by material evidence, is it not permissible to suppose that, since it would 



* Since completing the manuscript of this paper, the authors have had the opportunity 

 of consulting Bracy Clark's work (14) on the Oestridae. In the hatching of the eggs 

 of G. intestinalis, he states how he found that moisture and friction were necessary, and 

 that these conditions were supplied when the host licked the eggs. As for the stimulus 

 which causes the horse to lick the eggs, Clark advances the ingenious theory that the 

 irritable biting of other flies, which he enumerates as Oonopes, Tabani, and "Muscae, is 

 responsible, and indeed, is of the opinion that the great majority of the larvae reach 

 the mouth in this way. It is undoubtedly true that Stomoxys by its attacks will furnish 

 this stimulus. The author also mentions the liability to infestation when one horse 

 performs the friendly operation of licking the egg-infested coat of another. 



As regards the eggs of 0. haemorrhoidalis, Clark was the first to observe that they were 

 deposited on the hps and that they were of a darker colour than those of O. intestinalis 

 or O. nasalis. 



Up to the time of appearance of Clark's paper the three species of Gastrophilus had 

 been hopelessly confused with each other and with Uypoderma. The author rendered 

 a material service to entomology by giving clear descriptions of the flies, accompanied 

 by excellent illustrations, thus enabling one to discriminate the three species readily. 



