176 



THE EVOLUTION OF SEX. 



II. Regeneration. — Spades and knives are not exactly instru- 

 ments of Nature, but they have their counterparts. Fighting with a 

 rival a crab may lose its claw, or the same may happen in the 

 frequently fatal molting, which seems almost like a mistake in Nature. 

 Slowly, however, forgiving Nature makes good the loss; the cells of 

 the stump multiply, and arrange themselves in obedience to the same 

 necessities as before, and a limb is regenerated. Many an appendage 

 among the lower animals is from time to time nipped off, only to be 

 grown again. A snail has been known patiently to regenerate an 

 amputated eye-bearing horn twenty times running. Sometimes one is 

 tempted to think that the animals almost understand that it is better 

 for one member to perish than for the whole life to be lost, so readily 

 does a starfish surrender an arm, or a lizard its tail. Yet it must be 

 recoo-nized that animals, like men, are often wiser than they wot of. 

 In the panic of capture, strong convulsions may occur, which surprise 

 and perhaps shock the molester of a sea-cucumber by the ejection 01 



Fig. 52. — The formation of a Sponge Colony (Olynthus) 

 by budding. — After Haeckel. 



its viscera; or a tetanic contraction of the muscles makes the slowworm 

 brittle in the hands of its captor. The power of regeneration is most 

 marked in echinoderms, but persists as high up as reptiles. The 

 regrowth of part of a lizard's leg is the chef-d'oeuvre in this line. 

 Beyond that, regeneration is restricted to little things. We constantly 

 regenerate the skin of our lips, but we can not naturally replace an 

 amputated limb. It is more marvelous that we can not, than that the 

 lizard can. That the cells of an irritated stump should divide and 

 multiply, and that the result should be the same as it was at the first, 

 is really no marvel, or rather as much as but no more than the original 

 development. The dividing cells of the growing stump are simply 

 repeating their original development. 



III. Degrees of Asexual Reproduction. — The keynote of the 

 subject was truly struck by Spencer and Haeckel, when they defined 

 asexual reproduction as discontinuous growth. All growth is a 



