170 MISCELLANEOUS OBJECTIONS TO THE [CHAP. VIL 



and this chiefly in colour. Assuming that an insect originally 

 happened to resemble in some degree a dead twig or a decayed 

 leaf, and that it varied slightly in many ways, then all the 

 variations which rendered the insect at all more like any such 

 object, and thus favoured its escape, would be preserved, whilst 

 other variations would be neglected and ultimately lost; or, if 

 they rendered the insect at all less like the imitated object, 

 they would be eliminated. There would indeed be force in Mr. 

 Mivart's objection, if we were to attempt to account for the above 

 resemblances, independently of natural selection, through mere 

 fluctuating variability ; but as the case stands there is none. 



Xor can I see any force in Mr. Mivart's difficulty with respect 

 to "the last touches of perfection in the mimicry;" as in the 

 case given by Mr. Wallace, of a walking-stick insect (Ceroxylus 

 laceratus), which resembles "a stick grown over by a creeping 

 moss or jungermannia." So close was this resemblance, that a 

 native Dyak maintained that the foliaceous excrescences were 

 really moss. Insects are preyed on by birds and other enemies, 

 whose sight is probably sharper than ours, and every grade in 

 resemblance which aided an insect to escape notice or detection, 

 would tend towards its preservation; and the more perfect the 

 resemblance so much the better for the insect. Considering the 

 nature of the differences between the species in the group which 

 includes the above Ceroxylus, there is nothing improbable in this 

 insect having varied in the irregularities on its surface, and in 

 these having become more or less green-coloured ; for in every 

 group the characters which differ in the several species are the 

 most apt to vary, whilst the generic characters, or those common 

 to all the species, are the most constant. 



The Greenland whale is one of the most wonderful animals in 

 the world, and the baleen, or whale-bone, one of its greatest 

 peculiarities. The baleen consists of a row, on each side, of the 

 upper jaw, of about 300 plates or laminae, which stand close 

 together transversely to the longer axis of the mouth. Within the 

 main row there are some subsidiary rows. The extremities and 

 inner margins of all the plates are frayed into stiff bristles, which 

 clothe the whole gigantic palate, and serve to strain or sift the 

 water, and thus to secure the minute prey on which these great 

 animals subsist. The middle and longest lamina in the Greenland 

 whale is ten, twelve, or even fifteen feet in length ; but in the 

 different species of Cetaceans there are gradations in length ; the 

 middle lamina being in one species, according to Scoresby, four 

 feet, in another three, in another eighteen inches, and in the 

 Balaenoptera rostrata only about nine inches in length. The 

 quality of the whale-bone also differs in the different species. 



