120 RETROGRESSION 



the amount and complexity of this intra-uterine preparation. 

 Even after birth the young of the higher animals are protected to 

 give time for still more development, still more recapitulation, 

 particularly that development which results physically from use 

 and mentally from that synonym for use, experience. Such young 

 animals, owing to the decay (precisely similar to that observable 

 in the embryo) of faculties, especially instincts, present in the 

 ancestry, are incapable of maintaining independent existence. In 

 brief, whenever the active struggle is abolished, the structures and 

 faculties by which it was maintained tend to disappear, except in 

 so far as they serve as foundations on which are reared characters 

 that are useful later in the battle of life. 



198. Animals comparatively low in the scale of life, many 

 insects for instance, do not protect their young after birth. More- 

 over, birth occurs at an early period of development that is, 

 when offspring have recapitulated nothing or comparatively little 

 of the life-history. But very complex and rapid development 

 occurs during the quiescent period in the egg-case. To take the 

 familiar example of the butterfly the caterpillar when he emerges 

 has already undergone development in which he has recapitulated 

 a vast phase of the evolution of his race. Next, for a long period, 

 during which an active life is led, very few structural alterations, 

 except increase in size, occur. Probably during this active time 

 the environment, speaking relatively, very nearly resembles the 

 ancestral environments, and the caterpillar his remote ancestors 

 who developed no further. Doubtless he differs from them, but 

 not to the extent that the embryo in the egg-case differs from 

 the ancestors it represents. The structures and faculties have not 

 undergone the same amount of retrogression ; the life-history is 

 recapitulated in greater detail. The function of this active period 

 is the accumulation of nutriment which furnishes material both for 

 the growth of the caterpillar and for his subsequent developments. 

 Next comes another period of quiescence in the chrysalis, which 

 again affords opportunity for great retrogression and, therefore, 

 for the later phases of the life-history to be very rapidly retold. 

 In this period occur changes which swiftly recapitulate the evolu- 

 tion that added an aerial stage to the development of a hitherto 

 purely terrestrial insect. In the last, the active butterfly stage, 

 however long it may endure, there is again complete, or almost 

 complete cessation of structural alteration. 



199. The quiescent periods of development in the egg-case and 

 the chrysalis are strictly homologous to the period of intra-uterine 



