PACKARD. — INHERITANCE OF ACQUIRED CHARACTERS. 365 



stage the tubercles still persist, but the markings differ very much, as 

 reddish dorsal patches appear in the middle and near the end of the 

 body, and there are anticipations of the markings of the fully grown 

 caterpillar. In the present stage the insect closely resembles the 

 mature larva, having bright crimson markings on the thoracic seg- 

 ments, and on the third and fourth and on the fifth and sixth abdomi- 

 nal segments, these bright spots becoming somewhat less decided and 

 conspicuous in the final stage. 



Now it seems natural to suppose that the disappearance of the 

 armature of this insect with the first moult was due to the lack of need 

 for it by the caterpillar, which gradually became adapted to a life on 

 the under side of an oak leaf, where it assumed a simple spindle- 

 shaped body, extended when at rest along the midrib, in which posi- 

 tion we have found such caterpillars, its body glaucous green, and so 

 marked with yellowish lines and reddish spots, as well as with dashes 

 and lines, as to be wonderfully assimilated to the greenish, reddish, and 

 whitish hues and shades of the leaf under which it was sheltered. 



It also seems reasonable to suppose that these adaptational colora- 

 tional features were acquired by the ancestors of the present forms 

 during the different stages succeeding the first ecdysis. And thus we 

 are warranted in assuming that this and multitudes of other cases of 

 adaptation to the change in habits and modes of life, and special situa- 

 tions, were acquired originally at different periods after birth during 

 an earlier geological period than this, when the ancestors were fewer 

 in number and more plastic than now. Otherwise, how can we have 

 had the differentiation of a few ancestral forms into the present series 

 of genera, subfamilies, and families, represented by such a great 

 number of species ? 



Indeed, it seems diffcult to account for the evolution of the vast 

 hordes of existing species of insects unless we assume that there was 

 going on throughout the entire process the rise and perfecting of post- 

 natal acquired characters, such characters becoming fixed by heredity, 

 and reappearing with unerring certainty at different stages in the life 

 of the individual ; while in some animals whose postnatal metamor- 

 phosis through some environmental change became suppressed, we 

 have the more salient stages epitomized during the life of the 

 embryo.* 



* For many additional facts in the ontogeny of the Bombycine moths bear- 

 ing on this subject the reader may be referred to my papers in the Proceedings 

 of the Boston Society of Natural History, XXIV. 510-560, 1890 ; Journal of the 



