A CONTRIBUTION TO THE KNOWLEDGE OF BOT-FLIES. 105 



Of the recently emerged larvae, that of G. intestinalis is largest in size and 

 G. haemorrhoidalis smallest. In these two species there are 13 body segments, whilst 

 G. nasalis has but 12 and is the only one bearing slender, elongate hairs. The larval 

 posterior spiracles of the latter species are sessile ; whereas in the others the two 

 spiracles are borne on the distal ends of two cylindrical processes arising from the 

 ultimate abdominal segments. 



The eggs of G. intestinalis do not readily hatch unaided, but apparently require 

 the application of moisture and friction or shock. A large number of nasalis eggs 

 hatched spontaneously and a few of the haemorrhoidalis eggs also. This latter fact 

 is regarded as supporting the theory that the newly emerged larvae of these two 

 species may penetrate directly into the integument of the host. The lesions on 

 the skin of the intermaxillary space and lips of the host observed at the time the 

 eggs were hatching may be due to direct penetration of the larvae of nasalis and 

 haemorrhoidalis respectively. 



The newly emerged larvae of intestinalis failed to penetrate the hair-bearing integu- 

 ment of the host, but positive results were obtained when they were placed on portions 

 of the buccal mucosa of a horse and calf recently killed. A larger number suc- 

 ceeded in penetrating the papillated portion of the calf's tongue, as compared with 

 the unpapillated. 



The three species are probably present in each of the western provinces of Canada. 



As regards their seasonal appearance, intestinalis is somewhat later than nasalis 

 and haemorrhoidalis, which appear simultaneously and are on the wing for about 

 the same time. G. intestinalis continues to be active far into the autumn. 



Of the three species, intestinalis causes the animal less apprehension than the other 

 two. 



The provision of leather-flaps on the lips of the horse, cut into strips, comb-wise, 

 is advocated as likely to give good results in warding off the attack of 

 G. haemorrhoidalis. 



Acknowledgments. 



The authors desire to render their grateful thanks to Dr. W. C. Murray, President 

 of the University of Saskatchewan, for the laboratory accommodation which he so 

 kindly granted. They are also indebted to Mr. T. N. Willing, Professor of Natural 

 History in the University, for his generously allowing them to consult the specimens 

 of Oestridae in his collection. 



Ottawa, 28th November 1917. 



Literature. 



1. Hadwen, S. — A further Contribution on the Biology of Hypodertna lineatum. — 

 Bull. No. 21, Health of Animals Branch, Dept. of Agr., Ottawa, 1916. 



2. Carpenter, G. H., Hewitt, T. R., & Reddin, T. K — The Warble Flies ; Report 

 of Experiments and Observations as to Life-History and Treatment. — Jl. Dept. 

 Agr. and Tech. Instr., Ireland, XV, 1914, pp. 105-132. 



3. Roubaud, E. — Auto-inoculation et developpement primaire dans les muqueuses 

 buccales, de la larva du Gastrophile equin (Oestre du cheval). — OR. Acad. Sciences, 

 Paris, CLXIV, 1917, pp. 453-456. 



