10 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



II. THE LARVAL ARMATURE OF THE CERATOCAMPINiE. 



The armature of lepidopterous larvie consists either of glandular hairs or seta?, tactile hairs, 

 and defensive spines, and in function are either glandular or simply tactile, or both functions 

 combined, or are defensive, the base of the spines of larva? of the group Cochliopodidie being 

 glandular and secreting an active poison. The setie are seci'eted by unicellular dermal glands. 



The base of the seta is strengthened by the deposition of chitin or parenchyma so as to form 

 a pediment or support of the seta, and as a rule the size of the wart or tubercle thus formed is 

 correlated with that of the seta or spine arising from it. 



Change of function in the armature. — While the primitive function of the hairs, judging 

 from the fact that they appear to have arisen in freshly hatched lai'vie of the more primitive 

 groups of Lepidoptera, though present in the first stage of butterfly larva and in Notodontida?; 

 they also at the same time served as tactile or sense-hairs. Then from l^eing simply tactile they, 

 by use or as the result of external stimuli resulting from the attacks of other insects, etc., 

 became so strengthened, chitinized, and spiny as to render the animal unpalatable or inedible, as 

 nearly if not all hairy caterpillars are known to be. 



A final step was the secretion of an acrid pungent poison at the base of the spine, as notably 

 in the case of the Megalopygida;, Liparidte, Hemileucida?, and Saturniidse." 



The glandular hairs occur on the larva^ of Pterophorida? (Dimmock). I have observed them in 

 the first larval stages of Platypterycidcij and Notodontidfe, as well as certain Sphingidre {Deidauiia 

 insculptuni and Ampelophaga m}jron)\ also in the Saturniida? (Attacinaj); also in Ceratosia 

 tricoliyr. According to Scudder, in his work on the Butterilies c)f the Eastern United States, they 

 occur on the freshlj- hatched larva of the Nyiuphalidte, Lycwnidte, and certain Papilionidw 

 {Papilio cresphontes), Piei'lnse, and Hesperidi».* 



Origin of the tuhercles or tubercular hase of the hrivtie or setm. — Not only in lepidopterous 

 larvEB, but also in those of other orders, especially certain larval Coleoptera and Panorpidie, 

 do the setse arise from a swollen, fleshy, or chitinous base forming a wart or tubercle. When 

 giving ofl' a hair or bristle such tubercles are referred to as setiferous. Theoretically the swollen 

 base of the hair (see Part I of this Monogi'aph, PI. XXVI, tig. 11) is apparently due to the motion of 

 the long slender hair in touching objects, as the caterpillar creeps among the leaves of its food 

 plant. Such motions and stimuli lead to the aggregation of tissue around the base of the seta, 

 serving to support it. The simple primary seta with its conical tubercle may lose its functions and 

 atrophy so as to leave only the tubercle, which may be soft, fleshy, as in certain Notodontidse in 

 which the}' are nutent, and thus fitted Ijy their slight movements to ward oft' or at least deter 

 parasitic insects from ovipositing on them. On the other hand, the tubercle maj', as in the Cerato- 

 campidse, become converted into a purely defensive horn-like spine, with branches like a deer's 

 horn, as in Eacles and Citheronia, etc. The horn-like spines on the prothoracic segment of Hetero- 

 campa are remarkable from their apparently sporadic occurrence in a group which are as a rule 

 not provided with spinous protections. 



Arrangement <f the Setiferous tuhercies in Lej>i(?opte7-a .-^WhWe the larvre of certain Cole- 

 optera, Diptera, Panorpidaj, etc., are hairy and. as in Panorpidw, arise from a swollen conical 

 base, i. e., a tubercle, their special arrangement in the Lepidoptera is, so far as known, diagnostic 

 of the order. 



In the Panorpidie, which, in some important respects, are allied to what may have been the 

 ancestral stock of the Lepidoptera, the setfe, judging by Brauer's figures of the first and final stages 



« For notes on the armature of various families of moths see Proc. Amer. Phil. See. xxxi, 1893, pp. 83, 139. 

 '' See my Notes on some points in the external structure and phylogeny of lepidopterous larvte. Proc. Boston 

 Soc Nat. Hist., May, 1900, pp. 83-114. 



