1901.] 95 



removed from the s[)iiial f;iii:il of cattle and inserted beneath tlie skin 



of a dog and of a goat, while other simihir larvae were introduced into 



the oesophagus of two other dogs aud of a rabbit, Koorevaar carne to 



the conclusion that — 



" The young larvEE of Hypoderma boi-is at first pass beiieatli the skin, and 

 froiu thence betake tliemselves to the spinal canal and other places, to return later 

 into the subcutis, and there undergo furtiier development under the well-known 

 conditions " (Ann. Mag., loc. cit., p. 73). 



It follows that if we accept the conclusions of both Koorevaar 

 aud Riley, there is a striking dift'erence between the life-histories of 

 Hypoderma hovis and H. lineatum, in that, while the larvse of both 

 ultimately form warbles beneath the skin of cattle, in the earliest 

 stage the larvje of the former gain access to the host by boring their 

 way through the skin (as was formerly believed to be the case in all 

 species of Hypoderma), while those of the latter do so via the mouth 

 and the wall of the oesophagus. Koorevaar's opinion, however, was 

 due to finding that while the larva? inserted beneath the skin 

 " wandered about into various places agreeing with those in which 

 they are found in cattle," the introduction of larvte per os produced 

 a negative result, in that all trace of the larvte disappeared. In con- 

 nection with this it may be pointed out, however, that since, as is 

 shown in the extract from Riley quoted above, the just-hatched larva 

 of Hypoderma lineatum is armed with spines, which enable it to pierce 

 the CEsophageal wall, while in the subsequent stage in which it travels 

 about in the tissues of its host its integument is smooth, it may well 

 be that the spinal larva of R. bovis is unable to make its way through 

 the tough wall of the oesophagus, although it may have done so in 

 the previous stage. It is scarcely likely that between the life-histories 

 of two closely allied species such a striking difference should exist as 

 that indicated above, but, as has been shown, the conclusions of 

 Koorevaar and Riley are not necessarily antagonistic. Enough has 

 been said, however, to enforce the statement at the commencement of 

 this paper, and to show that any student of natural history, who 

 happens to live in a district in which either or both of our British 

 Cattle Warble-Flies occur, might do really useful work by taking the 

 hint. It is scarcely necessary to remark that should Hypoderma hovis 

 be found, like H. lineatum, to be in the habit of depositing its eggs 

 on the hair round the pasterns, there would, in the case of this species 

 also, be strong presumptive evidence in favour of Prof. Riley's view. 



British Museum (Natural History), 

 London, S.W. : 



February 20th, 1901. 



