38 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



aiicestral forms iuto the present series of genera, subfamilies, and families represented by siicli a 

 great number of species? 



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

 insects, iinless we assume that there was going on throughout the entire process the rise and 

 gradual perfecting of ])ostuatal acquired characters, such characters becoming flxed by heredity 

 and reappearing with unerring certitude at difterent stages in the life of the individual, while in 

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

 ei)itomized during the life of the embryo. 



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

 of these Notodontians are, as shown by the experiments of Wood, and especially of Poulton, the 

 result of the environment, being due to the action of the 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 physiological processes. The skin is spotted and painted by 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 produced 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 tluis acquired in 

 the larva at a certain stage in the life of the individual, 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 off and 

 be"-inning to be variously spotted and tinted, there is made ready the peculiar en vironment of these 

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

 Ave shall continue to have similarly spotted caterpillars; should the leaves remain green, we should 

 not expect to have such spotted larvie. Now, these changes in the larva' 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 production is attributed to "natural selection,"' as if it were the main and only efficient cause 

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

 produced, 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 after the new 

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

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

 subordinate factor to preserve the organism. 



Family Cendommp'ulw.—lt is easy to believe that this group might have evolved from such a 

 thoroughly armed caterpillar as that of Hetcrocampa guttiritta, ^\ho>ie ontogeny we have just out- 

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

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

 the case of SpUhujicampa bicolor, a creature of marvellous beauty of ornamentation, which feeds 

 on the Gleditschia 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 THE ONTOGENY OF SPHINGICAMPA BICOLOR. 

 A. CONGENITAL CHARACTERS OF THE LARVA, ALL AITKARIXG IX STAGE I. 



1. The two pairs of enormous spines of second and third thoracic segments one-half as long 

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

 defensive in function. 



2. The large, reddish, spiny "caudal horn" on the eighth uromere ending in two bristles. 



