Animal Galls. 429 



each other like a pocket spy ing- glass, which this fly, like 

 others, has a power of contracting at pleasure."* 



In another work he is still more explicit. "This well- 

 known fly," he says, " hovers the whole day over the back of 

 the reindeer, with its tail protruded and a little bent, upon 

 the point of which it holds a small white egg, scarcely so 

 large as a mustard-seed, and when it has placed itself in a 

 perpendicular position, it drops its egg, which rolls down 

 amongst the hair to the skin, where it is hatched by the 

 natural heat and perspiration of the reindeer, and the grub 

 eats its way slowly under the skin, causing a bump as large 

 as an acorn. "f The male and female of the reindeer breeze- 

 fly are figured in the * Library of Entertaining Knowledge, 

 Menageries,' vol. i. p. 405. 



There is one circumstance which, though it appears to us 

 to be of some importance in the question, has been either 

 overlooked or misrepresented in books. " While the female 

 fly," say Kirby and Spence, " is performing the operation of 

 oviposition, the animal attempts to lash her off as it does 

 other flies, with its tail ;" J though this is not only at variance 

 with their own words in the page but one preceding, where 

 they most accurately describe " the herd with their tails in 

 the air, or turned upon their backs, or stiffly stretched out 

 in the direction of the spine," but with the two facts 

 mentioned above from Eeaumur, as well as with common 

 observation. If the ox then do not attempt to lash off the 

 breeze-fly, but runs with its tail stiffly extended, it affords 

 a strong presumption that the fly terrifies him by her 

 buzzing (asper, acerba sonans), rather than pains him by 

 piercing his hide : her buzz, like the rattle of the rattle- 

 snake, being instinctively understood, and intended, it may 

 be, to prevent an over-population, by rendering it difficult to 

 deposit the eggs. 



The horse breeze-fly (Gasterophilm equi, LEACH), which 



* Linnaeus, Lachesis Lapponica, July 19th. 



f Linnaeus, Flora Lapponica, p. 378, ed. Lond. 1792. 



J Kirby and Spence, Introd. i. 151. 



Ibid. p. 149. 



