MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



37 



Now, it seems uatural to suppose tbat the disappearance of the armature of this iusect with 

 the fust molt was due to the hick of need for it by the caterpilhir, wliieli gradually became adapted 

 to a Ufe 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 

 ji'laucons-green and so marked with yellowish lines and reddisli spots, as well as with dashes 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 stages of Jletei-ocaiiiva obUqxta and H^guttivitta. — I. Reterocavipa ohliqna Pack — Freslily batched larva; 7a, dorsal 

 vie^w ; 1 b, spine on third ; Ic, spine on i-ighth ; Jd, spine on ninth abdominal segment ; le, prothoracic horns of stage I, enlarged. II. Hetero- 

 ranipa obliqua Pncit.— Stage II; Ila, horns on first prothoracic segment. III. lletemcampa guttiritta TTaU-.— Horns in stage I; a, pro- 

 thoracic hum; h. one on second abdominal; c, one on third to fifth, and (?, on ninth ;ibdominal segment. (The seta; are in some cases omitted). 



It also seems reasonable to suppose that these adaptational, colorational features were acquired 

 by the ancestors of the present forms during the different stages succeeding the tir.-t 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 

 iu number and more plastic than now. Otherwise, how can we have the difl'erentiation of a few 



