VI DIFFICULTIES AXD OBJECTIONS 137 



a danger to the animal in passing rapidly through dense 

 thickets. But Sir James Hector states, that the wapiti, in 

 Xorth America, throws back its head, thus placing the horns 

 along the sides of the back, and is then enabled to rush 

 through the thickest forest Avith great rapidity. The brow- 

 antlers protect the face and eyes, while the widely spreading 

 horns prevent injury to the neck or flanks. Thus an organ 

 which was certainly developed as a sexual weapon, has been 

 so ouided and modified durino; its increase in size as to be of 

 use in other ways. A similar use of the antlers of deer 

 has been observed in India. ^ 



The various classes of facts now referred to serve to show 

 us that, in the case of the two higher groups — mammalia 

 and birds — almost all the characters by which species are 

 distinguished from each other are, or may be, adaptive. It is 

 these two classes of animals which have been most studied 

 and whose life-histories are supposed to be most fully known, 

 yet even here the assertion of inutility, by an eminent 

 naturalist, in the case of two important organs, has been 

 sufficiently met by minute details either in the anatomy or in 

 the habits of the groups referred to. Such a fact as this, 

 together with the extensive series of characters already 

 enumerated which have been of late years transferred from 

 the " useless " to the " useful " class, should convince us, that 

 the assertion of " inutility " in the case of any organ or 

 peculiarity which is not a rudiment or a correlation, is not, 

 and can never be, the statement of a fact, but merely an 

 expression of our ignorance of its purpose or origin.- 



1 Nature, vol. xxxviii. p. 328. 



- A very remarkable illustration of function in an apparently useless 

 ornament is given by Semper. He says, "It is known that tlie skin of 

 reptiles encloses the body with scales. These scales are distinguished by 

 very various sculpturiugs, highly characteristic of the different species. 

 Irrespective of their systematic signiticauce they appear to be of no value in 

 the life of the animal ; indeed, they are viewed as ornamental without regard 

 to the fact that they are microscopic and much too delicate to be visible to 

 other animals of their own species. It might, therefore, seem hopeless to show 

 the necessity for their existence on Darwinian principles, and to prove that 

 they are physiologically active organs. Nevertheless, recent investigations on 

 this point have furnished evidence that this is possible. 



" It is known that many reptiles, and above all the snakes, ca.st off the 

 whole skin at once, whereas human beings do so by degrees. If by anj' 

 accident they are prevented doing so, they infallibly die, because the old 



