38 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



ancestral forms into the itreseiit series of genera, subfamilies, and families represented by such a 

 great number of species? 



Indeed, it seems difficult to account for the evolution of the vast hordes of existing species of 

 insects, unless we assume that tliere was going on throughout the entire prcjccss the rise and 

 gradual perfecting of postnatal acquired characters, such characters becoming tixed by heredity 

 and reappearing with unerring certitude at dift'erent stages in the life of the individual, while in 

 some animals whose postnatal metamorphosis became suppressed we have the more salient stages 

 epitomized during the life of the embryo. 



Tlie reddish and russet spots developed in the three, and especially two, last stages of tlio larva 

 of these Notodontians are, as shown by the experiments of Wood, and especially of I'oulton, the 

 result of the environment, being due to the action of tlie color of the spots of the leaves on the 

 sensitive portions of the skin or cuticle of the caterpillars. It seems to be fundamentally due to 

 the action of both physical and jihysiological processes. The skin is spotted and painted l)y the 

 reflection of the red and russet tints of the leaves on the sensitive skin of the living organism. 



The results are inherited at a corresponding period of life, just as the tubercles, spines, horns, 

 and other kinds of armature. Hence for thousands of generations we have had such spotted 

 caterpillars. Now if, as is quite obvious, the spots are thus suddenly produced, since light and 

 dark hues were so i^roduced in Mr. Poulton's laboratory, at a certain time in the life of the cater- 

 pillars observed by him, as we know by his experiments the colors were produced in the individuals 

 of a single generation, it would seem to follow that in nature the characters were thus acquired in 

 the larva at a certain stage in the life of the indiviihml, and have been transmitted by homochronous 

 inheritance. Moreover, this appears to be a case where the characters have been produced by 

 the direct action of the environment. 



At the time, the last of summer, when the leaves are fully mature, preparing to fall oft" and 

 beginning to be variously spotted and tinted, there is made ready the peculiar environment of these 

 leaf-feeding larva% and so long as these conditions of red and russet spotted or tinted leaves exist 

 we shall continue to have similarly spotted cateri)illars; should the leaves remain green, we should 

 not expect to have such spotted larvai. Now, these changes in the larvre are due to the primary 

 factors of organic evolution, i. e., to changes in the environment, to the reflection of these bright 

 or russet colored patches on the cuticle of the animal. By the neo Darwinian, the organization 

 and i)roduction is attributed to "natural selection,"' as if it were the main and only eflicient cause 

 of evolution, but really it is not so at all. It may act as a subordinate factor after the colors are 

 2iroduced, and serve to preserve those individuals most distinctly marked, those less so more 

 readily falling a prey to birds and insects. Natural selection does not originate, but alter the new 

 structures or markings have appeared, as the result of the operation of the primary factors of 

 organic evolution (the views of neo-Lamarckiaus), natural selection comes in as a late and quite 

 subordinate factor to preserve tiie organism. 



Family Cerafocampitlw. — It is easy to believe that this grou]) miglit have evolved from such a 

 thoroughly armed caterpillar as that of Hetcrocampa guttimtta, whose ontogeny we have just out- 

 lined, as all the Ceratocampida' bear spines which vary in degree of c<unplexity. We are now 

 acquainted with the life history of each important genus of this interesting group. We will select 

 the case of Sphimikampa hicolor, a creature of nuirvellous beauty of ornamentation, which feeds 

 on the (lleditschia or spiny locust. After a detailed study of the larva through its first larval 

 stages to its maturity, we have drawn up the following summary of the more salient features in 

 its ontogeny, dividing the characters into those 'which are congenital and those which we believe 

 to have been acquired during the stages succeeding the first: 



SUMMARY OF THE SALIENT FEATURES IN TIIE ONTOGENY OF SPIIINGICAMPA HICOLOR. 

 A. CONGENITAL CIIARACTKRS OF TIIK I.ARVA, A 1,1. Arl'KAUINd IX STAGE I. 



1. The two pairs of enormous spines of secfuid aiul tliird thoracic segments one-half as long 

 as the body and ending in a two-spined, large, flattened, dark bulb, freely movable and phiinly 

 defensive in function. 



2. The large, reddish, spiny "caudal horn" on the eightli uroniere ending in two bri.stles. 



