10 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



II. THE LARVAL ARMATURE OF THE CERATOCAMPIN^. 



Tlie ariiialiirc of Icpidoptenms larviv consists either of trliiniliiliU' hairs or setiv. tactile hairs, 

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

 conil)ined, or are defensive, the base of the spines of larvie of the group Cochliopodidw l)eing 

 glandular and secreting an active poison. The set:e are secreted 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 fund ion in the armature. — While the primitive function of the hairs, judging 

 from the fact that thev appear to have arisen in freshly hatched larv» of the more primitive 

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

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

 b^- use or as the I'esult of external stimuli resulting from the attack:^ 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 notal)ly 

 in the case of the Megalopygidas, Liparid;e, Hemileucidte, and SaturniidiV." 



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

 the first larval stages of Platypterycidaj and Notodontidse, as well as certain Sphingida? {Deidamia 

 inxculjAuni and Ampelophaga myroji); also in the Saturniidw (Attacina'); also in Ceratosia 

 tricolor. Accoi'ding to Scudder, in his work on the Butterflies of the Eastern United States, they 

 occur on the freshly hatched larva of the Nymphalidte, LycEenidfe, and certain Papilionidie 

 {Papilio eresphontes), Pierinte, and Hesperida?.* 



Origin of the tubercle-^ or tuhercidnr base of the brintle or »etx. — Not only in lepidopterous 

 larvae, but also in those of other orders, especialh' certain larval Coleoptera and Panorpida?, 

 do the setiB arise from a swollen, fleshy, or chitinous base forming a wart or tuliercle. "When 

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

 base of the hair (see Part I of this jNIonograph, PL XXVI, tig. Ih) 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 Notodontidie in 

 which they are nutent, and thus fitted by their slight movements to ward off or at least deter 

 l)arasitic insects from ovipositing on them. On the other hand, the tubercle may, as in the Cerato- 

 campidie. 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- 

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

 not provided with spinous protections. 



Arrangement of the netifei'ous tuheixles in Lepidoptera. — While the larva^ of certain Cole- 

 optera, Diptera, Panorpidfe, etc., are hairy and, as in Panorpida?, 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 Panorpida'. which, in some important respects, are allied to what may have been the 

 ancestral stock of the Lepidoptera, the seta\ 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. Soc. xxxi, 1893, pp. 83, 139. 

 '' See my Notes on some jioints in the external structure and phylogeny of lepidopterous larva>. Proc. Boston 

 Por. Nat. Hist., May, IIKIO, i>i'. s:!-"n4. 



