20 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



Coining;: now to tlii' <)ri},'iii of liuiiii)s. lixt'd or ino\iiblt', jiiul of spines, the ehniigc from herba- 

 ceous to arl)()real fecdiiij;- jiTounds doubtless affected not ouly the shape of the body, causing it iu 

 niauy cases to be tlii.»'k and tlesliy, but also led to a hyijcrtrophy of tlie piliferous warts conunon 

 to all lepidopterous larva'. The change was probably not necessarily due to the stimulus of the 

 visits and attacks of parasitic insects, l)ecause the low feeders are, if anything, at the ])resent day 

 at least, more subject to injury from them than arboreal caterpillars. The cau<e was probably 

 more pervasive and a result of a change of the euvironinent, such as is seen iu the growth of 

 thorns on desert ])lants, or the knees of tlie cypress and otlier water jtlants, or the aerial roots of 

 ochiils and other eitiphytes; and that tiiey may have originated with compaiative suddenness 

 seems probable when we bear in nund 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 ])lastic 

 tliau animals. 



If the reader will look at the recapitulations we have given at the end of the detailed life 

 histories of certain Notodontiaus, it will bi- seen that not only are there diflereiit a(hi])ti\e charac- 

 ters in tlie larval, ]>upal, and imaginal stages, but that the lar\a 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 C(Uicealed IVom observation. Many have glandular hairs, while the 

 tubercles are more or less uniform. 



2. Toward the end of Stage II and in Stage III they feed in exjiosed situations on the upper 

 side of the leaves, and at the same tiuui ai)pears the showy style of ornamentation both as regaids 

 colors, hairs, and tubercles, approximating to that of the mature caterpillar, whose life api)areMtly 

 is conditioned by its bright colors and bizarre trappings. 



The smooth-bodied, green larvip of Gluphisia, Xadata, Lophodoiita, etc., are the primary forms.' 

 Their shai)e, <'oloration, and retired habits ally them biologically to the larvic of the European 

 Panolin pinipcrda and other smooth bodied, green caterpillars with reddish or yellowish sti-ipes, 

 wliicli feed on trees. These smooth larvaj are, however, rare and exceptional, especially in Xorth 

 America. 



But now, owing to a change iu the euvironmeut, there arose a tendency to the hy])ertrophy of 

 the normal piliferous 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 hypertroi)hy of certain 

 of the tubercles was effected in a comparatively sudden period iu conseijuence of a comparatively 

 sudden change from herbs to trees, and (L') in response to a sudden exigency; (3) that the si)ines 

 and stiff, dense spinulated hairs were immediately useful in preventing the attacks of parasitic 

 insects, while (4) the |)oison glands at the base of the tubercles (in the Attaci. etc.) served to render 

 them distasteful to birds, (5) the bright colors serving as danger sigiuils. 



The Lamarckian factors (1) of change (both direct and indirect) in the milieu, {-) need, and 

 (.3) change of habit, and the now generally adoi>ted jjrinciple that a change of function induces 

 change iu organs^ and iu .some or many cases actually induces the hypertrophy 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.' 



' 1 ;uii liDWcvur iiicliiRMl, since writing tlif above, to legard |i:il:nia ;mil I",, ^icni iis tlic iiiiist [iriniitivo forms of 

 Notoilontiiiii.s, t\w sniootli-tmdiid l;iivie ol' Glupliisia Ijeiiig secondary ionl :i(lai)tive forms. 



- K. Marey : I.e trausformismc et la physiologic cxpi'-vinieiitale, Cours du College de Fiance. Kevne .scientiliiiue, 

 ■2" Sdrie, iv, 81S. (Function malics the organ, especially in the osseons and muscnlar systems.) 



Seo also A. Dobru : Der Irspniiig der Wirbelthiero nud das I'linei)! des rnnctionswechscls, Leipzig, 1875. 



■' It is pcssible that the close resemblauce of the warts, projections, and sjiiiies of certain .irboreal caterpillars 

 which so closely mimic the spines, leaf scars, and projections of tin- branches or twig^ or plants, has been brought 

 al)Out iu a way analogous to the production of spots and lines on the body of caterpillars. Darwinians attrilmte 

 this to the action i>f "jirotectivo mimicry," bnt this expression rather cxjiresses the result of a series of causes to 

 which we have iMubavored to call attention. The elleet of dark and light shades and the light and shade iu 

 liroduciug the stripes and bars of caterpillars are comparatively direct and manifest ; but how can thorns and other 

 jirojectious on trees ami shrubs alVect caterpillars directly? Given the origination by hyi)ertrophy of warts and 

 spines, and it is then easy to seo that b,v natural selection caterpillars may have finally become adajited so as to 

 mimic similar vegetable growths. Our object is to endeavor to explain thc^ causes of the jirimary growth and 

 development of such projections, i. e., to lay the foundation for the action of natural selectiou. 



