k; mkmoujs of the national academy of sciences. 



known the lurvii is hatclictl witli this pair of horns silono, and it is significant that they are 

 situated on the most exposed part of the body. 



Instate I the dorsal spines are throughout longest in ^1. /v'/Y//«/(Vi*7'.v (those of the third 

 Jioracif segment largest in this species), and in this respect this species is the most primitive or 

 nivirest its supposed Adelocephala ancestor; the dorsal spines are longest in .1. stigma, are shorter 

 in .1. srnatorid, and much the shortest in ^1. ruhicundd. 



It is noteworthy that in the full-fed larva the doi-sal iiorns of the second thoracic segment 

 are longest in A. inrginensis, shorter in A. senatoria, and shortest in ^1. rubkunda. 



The question arises as to the probable cause of the reduction in all the spines in this genus. 

 This may perhaps be answered by the fact that they do not need a defensive armature, owing to 

 the style of coloration, the body being striped, like so many unarmed caterpillars, especially 

 Noctuidiv, etc. J^Ioreover, the eggs are laid in large patches of over 200, the young larva? live 

 gregariouslv on the under side of leaves of the oak, maple, etc., which bear no spines, while this 

 gregarious habit in all but .1. nd>tcund<t is maintained throughout larval life, as they, especially 

 A. S'-natorat, are seen to be crowded together in clusters on the partly defoliated twigs of the 

 trees, somewhat after the manner of caterpillars of Datana. 



The snninal plate and it.s )iwd!f(yit!onx. — This is the reduced tenth abdominal segment, and 

 is flattened triangular, rather large, usually ending in a fork. 



In its perhaps most generalized form, that of Adelocephala hieolor, the suranal plate in stage I 

 is armed with three well-developed setiferous tubercles, the tubercles themselves conical but 

 higher than thick at the base, and bearing a long slender seta. The plate is forked at the end, 

 the two tei'minal tubercles giving it a forked appearance; there is also a pair of setiferous 

 tubercles similar in size and shape to the others, each one situated a little way in from the edge 

 and behind the middle. There ar<' no secondary setiferous tubercles. This description will also 

 apply to Syssphinx in its first stage. 



In the succeeding stage (II) and all the later stages the end of the plate is distinctly forked 

 and the surface of the plate is rough, with five secondary setiferous tubercles, while the primary 

 ones are but little larger than the secondary ones and merely hold their own in size; on the l)ase 

 of the two terminal tubercles forming the fork are several secondary setiferous tubercles. 



In the last stage the set* are much reduced in length, nearly atrophied in many cases, and 

 the surface of the plate is rather evenly granulated. 



In Anisota rnhicunda (Pis. LII, LlII) the suranal plate is rather short, rounded at the end, 

 iiaving lost the salient features of that of Adelocephala. The setiferous tubercles in stage I are 

 minute, though the bristles themselves are long, hair-like. The typical number is five on each 

 side, three marginal ones, one situated within, beyond the middle of the plate, and the pair of 

 terminal ones. After the first molt the pair of terminal tuljercles are much laiger than liefore, 

 giving the plate a forked appearance. In the last stage the primary tubercles are large, distinct, 

 and black-pigmented. 



In stage I of .1. nd,i<-inid<i and seiiateiria the plate is simplest; in A. etrij/niens/'s and »tigina 

 it is more specialized and somewhat pigmented. In the second to the final stages, however, of 

 A. aenatiii'la the plate is more stoutly spinose than in any other species, the lateral and two 

 terminal spines or tubercles being solid, conical, and pigmented brown black (fig. 2). 



In Eadex iinperiallx the armature of the suranal i)late is very formidable in the two first 

 stages (Pis. XLVIII. figs. 1, 2), especially before the first molt. The first tubercle, i. e., that 

 nearest the ninth segment, on each side is very large, four-headed, and as long as the entire plate. 

 In the second stage, the tubercle spines are reduced in size but retain the same structure, the 

 setiv remaining; but after the second molt the great basal spines become reduced to low, flattened, 

 broad, hubbly vestigial tubercles, with secondary tubercles. The plate is black in tlie last stage, 

 with the edges yellow, while the granulations, or low stout conical tuliercles, are coarse and 

 render the surface of the plate rough. 



In Oithei'onta regal isthe armature of the suranal plate is similai' to tliat of Eacles, on the same 

 plan, but tiic tubercles and theii- spinules are much longer and slenderer, as >een in PI. LIV, rigs. 



