516 DIPTERA 



CHAP. 



inferred from this that the fly places its eggs in this situation, 

 and as the cattle are known to dread and flee from the fly, it 

 was supposed to be on account of the pain inflicted when the egg 

 was thrust through the skin. Recent observations have shown 

 that these views are erroneous, but much still remains to be ascer- 

 tained. The details of oviposition are not yet fully known, 

 but it appears that the eggs are laid on the lower parts of the 

 body, especially near the heels, and that they hatch very speedily. 1 

 As the imago of Hypoderma appears for only a very short period in 

 the summer, the time of the oviposition is certain. The newly- 

 disclosed larva is considerably different from the more advanced 

 'instar found in the skin of the back ; moreover, a long period of 

 many months intervenes between the hatching of the larva and 

 its appearance in the part mentioned. Brauer has shown that 

 when the grub is first found in that situation it is entirely sub- 

 cutaneous. Hence it would be inferred that the newly-hatched 

 larva penetrated the skin probably near the spot it was deposited 

 on, and passed a period in subcutaneous wandering, on the whole 

 going upwards till it arrived at the uppermost part : that after 

 moulting, and in consequence of greater need for air, it then 

 pierced the skin, and brought its breathing organs into contact 

 with the external air ; that the irritation caused by the admission 

 of air induced a purulent secretion, and caused the larva to be 

 enclosed in a capsule. Dr. Cooper Curtice has however found, 

 in the oesophagus of cattle, larvae that he considers to be quite 

 the same as those known to be the young of Hypoderma ; and 

 if this prove to be correct, his inference that the young larvae 

 are licked up by the cattle and taken into the mouth becomes 

 probable. The larva, according to this view, subsequently pierces 

 the oesophagus and becomes subcutaneous by passing through the 

 intervening tissues. The later history of the grub is briefly, that 

 when full grown it somewhat enlarges the external orifice of its 

 cyst, and by contractions and expansions of the body, passes to 

 the surface, falls to the ground, buries itself and becomes a pupa. 

 If Dr. Curtice be correct, there should, of course, be as many, 

 if not more, larvae found in the oesophagus as in the back 

 of the animal ; but, so far as is known, this is not the case, and 

 we shall not be surprised if the normal course of development be 

 found different from what Dr. Curtice supposes it to be. His 



1 Riley, Insect Lift, iv. 1892, p. 302. 



