MEMOIKS OF THE NATIONAL ACADEMY OF SCIENCES. 



37 



Now, it seems uatural to suppose that the disappearauce of the armature of this insect with 

 the tirst molt was due to the lack of need for it by the caterpillar, which gradually became adapted 

 to a life on the underside of an oak leaf, where it assumed a simple spindle-shaped body extended 

 when at rest along the midrib, in which position we have found the older caterpillar, its body 

 glaucous-green and so marked with yellowish lines and reddish spots, as well as with daslies and 

 lines, as to be wonderfully assimilated to the greenish, reddish, and whitish hues of the leaf under 

 which it was sheltered. 



Fig. 1. — Early stiagrs of Hetemcainpa obliqva and II. fjuttivitta. — I. Heterocampa oblujita Paci. — Freshly batched larvaj 7a, dorsal 

 view; lb, spiue ou third ; ICy spine on eighth : Jd, spiue on cintli abdominal segment ; le, prothoracic horns of stage I, enlarged. II. Hetero- 

 canjpa obliqna Pack. — Stage 11; Ila, horns on fir.st prothoracic segment. III. Hclcrocampa gnttivitta Walk. — Horns in stage I; a, pro- 

 thoracic horn; h, one on second abdominal : c. one on third lo tilth, and rf, tin ninth abdominal segment. (Thosetffi are in some cases omitted). 



It also seems reasonable to suppose that these adaptatioiial, colorational 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 situations 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 the differentiation of a few 



