94 PROBLEMS OF EVOLUTION 



individual. A particular apteryx is born with a limited amount 

 of vital energy, and since he makes great use of his legs, this 

 will, no doubt, stream towards them, while other less important 

 organs will be impoverished. Can we say that in the case of a 

 species there is any such limitation ? When we speak of economy 

 of growth in a species or breed, I believe that what is meant 

 resolves itself into nothing more than this, that the difficulty of 

 forming a neiv breed is proportioned to the number of characters that 

 are required in combination. Kiwis, possessed of great strength of 

 leg and keenness of scent, were a more probable achievement of 

 evolution, so to put it, when strength of wing, combined with 

 these other qualities, was no longer insisted on. 



If I am right in holding that there is for a species no such 

 thing, strictly speaking, as economy of growth, then all the 

 examples of loss that might appear to fall under (2) are really 

 to be ranked under (3) as illustrating the shedding of things 

 useless though not injurious. 



( 3 ) to There are instances not a few of organs disappearing, though 

 pammixis they were so small that we can hardly suppose them capable of 

 bringing the organism into danger, or of taxing its resources. 

 In some whales no traces of hind-limbs have been found, though 

 Mr Beddard is of opinion that they may exist in all. The clavicle, 

 at any rate, seems to have disappeared entirely. " The white 

 whale, Beluga, and the Narwhal, Monodon, appear never to pos- 

 sess any hairs, either as adults or foetuses." l Not a sign of the 

 upper incisor teeth of ruminants is to be found, even in embryos. 

 Having first dwindled to insignificance, and become incapable 

 either of good or harm, they have finally vanished and left not a 

 wrack behind. In anophthalmus, the blind beetle of the Ken- 

 tucky caves, the whole machinery of sight has disappeared from 

 the optic lobes to the facets of the outer surface. In the cele- 

 brated blind cray-fish (Cambarus pellucidus), found in the same 

 caves, the optic lobes and the optic nerves persist : the retina has 

 degenerated. Vestiges are phenomena so common that we may 

 well hold that reduction in size proceeds more slowly when the 

 organ in question has already sunk to very minute dimensions. 



1 See Mr Beddard's Soot of Whales, pp. 24, 27, and 99. 



