Organic Evolution. 221 



element, and are developed under the auspices of in- 

 telligence or instinct. But the lower stages, the supply of 

 food-yolk and intra-uterine protection, are purely organic. 

 A hen cannot by instinctive or intelligent forethought 

 increase the amount of food-yolk stored up in the ovum, 

 any more than the lily, which, by an analogous process, 

 stores up in its bulb during one year material for the best 

 part of next year's growth, can increase this store by a 

 mental process. 



It cannot therefore be questioned that variations in the 

 amount of capital with which an embryo is provided in 

 generation would very materially affect its chances of 

 escaping elimination by physical circumstances, by enemies, 

 and by competition. 



Nor can it be questioned that variations in the time 

 occupied in reaching maturity would, other things equal, 

 not a little affect the chances of success of an organism in 

 the competition of life. Hence we have the phenomena 

 of what may be termed acceleration and retardation in 

 development. These terms have, however, been used by 

 American zoologists, notably Professors Hyatt and Cope, 

 in a somewhat different and wider sense ; for they include 

 not merely time-changes, but also the loss of old characters 

 or the acquisition of new characters. "It is evident," 

 says Professor Cope, "that the animal which adds some- 

 thing to its structure which its parents did not possess 

 has grown more than they; while that which does not 

 attain to all the characteristics of its ancestors has grown 

 less than they." " If the embryonic form be the parent, the 

 advanced descendant is produced by an increased rate of 

 growth, which phenomenon is called ' acceleration ; ' but if 

 the embryonic type be the offspring, then its failure to 

 attain the condition of the parent is due to the supervention 

 of a slower rate of growth ; to this phenomenon the term 

 'retardation' is applied." "I believe that this is the 

 simplest mode of stating and explaining the law of varia- 

 tion : that some forms acquire something which their 

 parents did not possess; and that those which acquire 



