40 
MEMOIES OF THE NATIONAL ACADEMY OF SCIENCES. 
it seems to be the type of a distinct subdivision of tlie Ceratocampidm (the subfamily Agliime)^ as 
we have named the group. This form is a coimecting link between the genuine Ceratocampidm 
and the Saturniidm. As originally shown by Duponchel and more recently by Mr. Poulton, before 
the last molt the caterpillar wholly discards the congenital characters, viz, its spinous armature, 
characters common to the Ceratocampidie, and assumes an entirely and strikingly different shape. 
It is now destitute of any spines at all, its body is rather short and thick, the segments full convex, 
and it closely ai^proximates the general appearance of a Saturnian larva, though the majority of 
these are armed with more or less spiuose tubercles; the caterpillar of the Brazilian Attacus hetis 
Walker, however, is iigured and described by Burmeister as being smooth-bodied. The Aglia is 
now quite a different creature from what it was in its earlier stages; its conditions of existence have 
somewhat changed, and in adaptation to such changes its means of defense are of a different nature. 
It now feeds passively on its food plant, and is dependent on its colors, various delicate shades 
of green and yellow, to escape the observation of its vertebrate and insect enemies, ami if discovered 
it appears to rely on its large, terrifying eye-spot and somewhat sphinx-like attitude to frighten 
away its aggressors. 
1^0 w, it seems most natural to suppose that the features of the last stage were in the ancestors 
of this insect acquired wholly or in part during a delinite e])Och in the lifetime of one or perhaps 
of a few generations. The mature characters were not originally congenital and would have 
perhaps been useless in the early stages of the caterpillar. They may have suddenly appeared in 
a single individual and then have become transmitted by heredity and fixed by natural selection, or 
this process may have extended through sev^eral, though not very many, generations. 
The chief factors in the origination of such a strikiug change in shape and ornamentation after 
the last molt appear to have been the atrophy of the spines and tubercles by disuse, the larva, by 
a change in its mode of life, with more sluggish habits and perhaps feeding in less exposed 
conditions, not needing them, the same change resulting in a transfer of the nutritive ffuids 
and bringing about the deposit of pigment in definite places, as in the eye-spots. 
Whether one accepts the view of the transmission of acqiiired characters or not, it must be 
conceded that the remarkable changes exhibited by Aglia in the last stage must have been 
induced with more or less suddenness; that the tendency, at least, to the change was probably 
originated during the lifetime of perhajjs a single individual. The case seems to us to almost 
amount to a crucial one, and if it can be explained by any other mode of reasoning than 
the one suggested it will be a matter of interest. Certainly the cougeuital characters show a 
remarkable contrast with what we assume to be acquired characters, and we know of no better 
examxde which could be cited to prove the fact of the transmission of acquired characters. 
Family Saixmiiidm , — lu the larval stages of this regal family we have great contrasts between 
the first aud later stages, both iu armature and coloration, as summarized below, each stage 
differing remarkably from the others: 
RECAPITULATION OF THE MORE SALIENT ONTOGENETIC FEATURES OF PLATYSAMIA OECROPIA. 
A. CONGENITAL CHAUACTEKS. 
1. The setfB iu Stage I blunt, slightly bulbous, and glandular. 
2. The tubercles are all of the same size. 
3. Body in Stage I dark, almost blackish green; head jet-black; tubercles yellowish green. 
4. The homologue of the “ caudal horn” shows iffainly its double origin. 
5. The difference between the colors of the larva of the first aud last stages very marked. 
B. EVOLUTION OF LATER ADAPTATIONAL FEATURES. 
1. The thoracic dorsal tubercles in Stage II aud onward are longer than the abdominal ones. 
2. Five rows of indistinct black spots along the body in Stage II, not so distinct as in S, cynthia^ 
the body being still dusky green. (These do not originate from lines.) At the end of Stage II 
the larva is more like cynthia of the same age, the body being more yellow aud the black spots 
more distinct. The spots disappear at the end of Stage lY. 
