300 THE ZOOLOGIST. 



elusion that they have not been limited in their scope to recent 

 times, but must have existed in past epochs, and even, to some 

 extent at least, in very remote epochs."* When gadflies are 

 about, the Ox " seems to be seized with an unreasoning paroxysm 

 of fear." " In modern times the gadfly merely causes some fear 

 and a little discomfort to an animal, and some loss of money and 

 temper to its owner when he finds that the hide has been per- 

 forated, and is therefore held cheap by the tanner. But there 

 must have been occasions when the war between gadflies and 

 cattle was a much more serious affair. So strongly marked a 

 protective instinct can only have been produced at a time when 

 the very existence of the species was threatened by parasites of 

 this order."f Sir Charles Lyell, as early as 1836, and before 

 much had been thought or expressed on the subject — for Darwin 

 had not then returned from his epoch-making voyage — appears 

 to have had clear conception of the phenomena, though based on 

 very different philosophical views to those he embraced and 

 enunciated later on. In a letter to Sir John Herschel, he ad- 

 vances probable causes that may aid a species' duration in time. 

 " Now, if it be an insect, it may be made in one of its trans- 

 formations to resemble a dead stick, or a lichen, or a stone, so as 

 to be less easily found by its enemies ; or, if this would make it 

 too strong, an occasional variety of the species may have this 

 advantage conferred upon it ; or, if this would be still too much, 

 one sex of a certain variety. Probably there is scarcely a dash 

 of colour on the wing or body of which the choice would be quite 

 arbitrary, or what might not affect its duration for thousands of 

 years. I have been told that the leaf-like expansions of the 

 abdomen and thighs of a certain Brazilian Mantis turn from 

 green to yellow as autumn advances, together with the leaves of 

 the plants among which it seeks for its prey. Now, if species 

 come in succession, such contrivances must sometimes be made, 

 and such relations predetermined between species, as the Mantis, 

 for example, and plants not then existing, but which it was fore- 

 seen would exist together with some particular climate at a given 

 time."! 



* S. H. Scudder, < Bull. U. S. Geol. Surv.' No. 124, p. 30 (1895). 

 f Louis Kobinson, ' Wild Traits in Tame Animals,' p, 150. 

 I 'Life, Letters, and Journals of Chas. Lyell,' vol. i. p. 468. 



