Organic Evolution. 219 



8. Variations in the period at which secondary sexual 

 characters and the maximum efficiency of the several 

 organs is reached. 



It is impossible here to discuss these modes of variation 

 seriatim. I shall therefore content myself with but a few 

 remarks on the importance of protection and fosterage. It 

 is not too much to say that, without fosterage and protec- 

 tion, the higher forms of evolution would be impossible. If 

 you are to have a highly evolved form, you must allow 

 time for its evolution from the egg; and that develop- 

 ment may go on without let or hindrance, you must supply 

 the organism with food and lighten the labour of self- 

 defence. Most of the higher organisms are slow in coming 

 to maturity, passing through stages when they are helpless 

 and, if left to themselves, would inevitably fall a prey to 

 enemies. 



In those animals in which the system of fosterage and 

 protection has not been developed a great number of 

 fertilized ova are produced, only a few of which come to 

 maturity. It might be suggested that this is surely an 

 advantage, since the greater the number produced the 

 greater the chances of favourable variations taking place. 

 But it has before been pointed out that these great numbers 

 are decimated, and more than decimated, not by elimina- 

 tion, but by indiscriminate destruction ; embryos, good, 

 bad, and indifferent, being alike gobbled up by those who 

 had learnt the secret of fostering their young. The 

 alternative has been between producing great numbers * of 

 embryos which soon fend for themselves, and a few young 

 who are adequately provided for during development. And 

 the latter have proved the winners in life's race. If we 

 compare two flat-fishes belonging to very different groups, 

 the contrast here indicated will be readily seen. The 

 skate is a member of the shark tribe, flattened sym- 



* In the third chapter we saw that in such cases not only are there an 

 enormous number of ova produced, but that (e.g. in aurelia'and the liver- 

 fluke) each ovum produces, through the intervention of asexual multiplica- 

 tion, many individuals. 



