20 
MEMOIRS OF THE EATIOifAL ACADEMY OF SCIENCES. 
9 
Coming now to the origin of humps, fixed or movable, and of spines, the clnuige from herba- 
ceous to arboreal feeding grounds doubtless alfected not only the shape of the body, causing it in 
many cases to be thick and lloshy, but also led to a hypertrophy of the piliferous warts common 
to all lepidopterous larvn\ The change was probably not necessarily due to the stimulus of the 
visits and attacks of parasitic insects, because the low feeders are, if anything, at the i)resent day 
at least, more subject to injury from them than arboreal caterpillars. The cause was probably 
more i)ervasive and a result of a (change of the environment, such as is seen in the growth of 
thorns on desert plants, or the knees of the cypress and other water plants, or the aerial roots of 
ochids and other ei>iphytes; and that they may have originated with comparative suddenness 
seems probable wlien we bear in mind the aerial roots of corn artificially produced in the lifetime 
of a single individual; though it should be taken into account that plants are far more plastic 
than animals. 
If the reader will look at the recapitulations we have given at the end of the detailed life 
histories of certain Notodontians, it will be seen that not only are there different adaptive charac- 
ters ill the larval, pupal, and imaginal stages, but that the larva itself in its different stages is 
wonderfully adapted to different surroundings. 
1. At first some, indeed most, species live socially on the underside of the leaves near where 
they were born, and thus concealed from observation. Many have glandular hairs, while the 
tubercles are more or less uniform, 
2. Toward the end of Stage II and in Stage 111 they feed in exposed situations on the upper 
side of the leaves, and at the same time appears the showy style of ornamentation both as regards 
colors, hairs, and tubercles, approximating to that of the mature caterpillar, whose life apparently 
is conditioned by its bright colors and bizarre trappings. 
The smooth-bodied, green larvm of Gluphisia, Xadata, Lophodonta, etc., are the primary forms,’ 
Their shape, coloration, and retired habits ally them biologically to the larvm of the European 
PanoUs xnniperda and other smooth-bodied, green caterpillars with reddish or yellowish stripes, 
which feed on trees. These smooth larvm are, however, rare and exceptional, esi)ecially in Horth 
America. 
But now, owing to a change in the euviroumeut, there arose a tendencj'' to the hypertrophy of 
the normal i)iliferous warts, and in the actual life history of the caterpillar the tendency manifests 
itself in the third stage of larval life. We are inclined to believe (1) that the hypertrophy of certain 
of the tubercles was effected in a comparatively sudden period in consequence of a comparatively 
sudden change from herbs to trees, and (2) in response to a sudden exigency; (3) that the spines 
.and stiff, dense spinulated hairs were immediately useful in preventing the attacks of parasitic 
insects, while (4) theqmisou glands at the base of the tubercles (in the Attaci, etc.) served to render 
them distasteful to birds, (5) the bright colors sei'ving as danger signals. 
The Lamarckian factors (1) of change (both direct and indirect) in the milieu, (2) need, and 
(3) change of habit, and the now generally adopted principle that a change of function induces 
change in organs'^ and in some or many cases actually induces the hypertroidiy and specialization 
of what otherwise would be indifferent parts or organs; these factors are all-important in the evo- 
lution of the colors, ornaments, and outgrowths from the cuticle of caterpillars."* 
' I am however inclined, since writing the iibovo, to regard Datuna and P.vgu^ra as the most primitive forms of 
^otodontiaus, the smooth-hodied larvie of Gluphisia being secondary and adaptive forms. 
R. Marey : Le transformismo et la physiologie expdrimentale, Cours du Coll^^ge de France. Revue scientifique^ 
2® S4rie, iv', 818. (Function makes the organ, especial^' in the osseous and muscular systems.) 
See also A. Dobrn: Der Ursprung der ’Wirbelthiere und das Princip des Fuuctiouswochsels, Leipzig, 1875. 
is possible that the close resemblance of the warts, projections, and spines of certain arboreal caterpillars 
which so closely mimic the spines, leaf scars, and projections of tlio branches or twigR or plants, has been brought 
about in a way analogous to the x)roductiou of spots and lines on the body of caterpillars. Darwinians attribute 
this to the actiou of “protective mimicry/’ but this expression rather expresses the result of a series of causes to 
which we have endeavmrod to call attention. The eflTect of dark and light shades and the liglit and shade in 
Xn’oduciug the stripes and bars of caterpillars are comparatively direct and manifest; but how can thorns and other 
projections on trees and shrubs affect caterpillars directlyf Given the origination by hyi)ertrophy of warts and 
spines, and it is then easy to see that by natural selection caterpillars may have finally become adapted so as to 
mimic similar vegetable growths. Our object is to endeavor to explain the causes of the jirimary growth and 
development of such projections, i. e., to lay the foundation for the action of natural selection. 
