758 THE POPULAR SCIENCE MONTHLY. 



cessive selections of favorable variations might have produced it ; and 

 the like holds of the no less remarkable appliance of the Venus's Fly- 

 trap, or the still more astonishing one of that water-plant by -which 

 infant-fish are captured. Though it is impossible to imagine how, by 

 direct influence of increased use, such dermal appendages as a porcu- 

 pine's quills could have been developed ; yet, profiting as the mem- 

 bers of a species otherwise defenceless might do by the stiffness of 

 their hairs, rendering them unpleasant morsels to eat, it is a feasible 

 supposition that from successive survivals of individuals thus defended 

 in the greatest degrees, and the consequent growth in successive gen- 

 erations of hairs into bristles, bristles into spines, spines into quills 

 (for all these are homologous), this change could have arisen. In like 

 manner, the odd inflatable bag of the bladder-nosed seal, the curi- 

 ous fishing-rod with its worm-like appendage carried on the head of 

 the lophius or angler, the spurs on the wings of certain birds, the 

 weapons of the sword-fish and saw-fish, the wattles of fowls, and 

 numberless such peculiar structures, though by no possibility explica- 

 ble as due to effects of use or disuse, are explicable as resulting from 

 natural selection operating in one or other way. 



In the second place, while showing us how there have arisen count- 

 less modifications in the forms, structures, and colors of each part, Mr. 

 Darwin has shown us how, by the establishment of favorable varia- 

 tions, there may arise new parts. Though the first step in the pro- 

 duction of horns on the heads of various herbivorous animals, may 

 have been the growth of callosities consequent on the habit of but- 

 ting — such callosities thus functionally initiated being afterward de- 

 veloped in the most advantageous ways by selection ; yet no explana- 

 tion can be thus given of the sudden appearance of a duplicate set of 

 horns, as occasionally happens in sheep : an addition which, where it 

 proved beneficial, might readily be made a permanent trait by natural 

 selection. Again, the modifications which follow use and disuse can 

 by no possibility account for changes in the numbers of vertebrae ; 

 but after recognizing spontaneous, or rather fortuitous, variation as a 

 factor, we can see that Avhere an additional vertebra hence resulting 

 (as in some pigeons) proves beneficial, survival of the fittest may make 

 it a constant character ; and there may, by further like additions, be 

 produced extremely long strings of vertebrae, such as snakes show 

 us. Similarly with the mammary glands. It is not an unreasonable 

 supposition that by the effects of greater or less function, inherited 

 tlirough successive generations, these may be enlarged or diminished 

 in size ; but it is out of the question to allege such a cause for changes 

 in their numbers. There is no imaginable explanation of these save 

 the establishment by inheritance of spontaneous variations, such as are 

 known to occur in the human race. 



So too, in the third place, with certain alterations in the connexions 

 of parts. According to the greater or smaller demands made on this 



