MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 15 



In Adelocephahi, after the tirst molt (PI. XLV. tig. 3), thoracic horns differ in the reduction 

 of the bulbs, which lose their swollen shape, bec'oming siuipl\- forked, and the rods becoming 

 mere sette. In the third and later stages there is a furtiier reduction of the two terminal spines, 

 the horns ending in a double point, with little signiticance. while the horns themselves become 

 shorter. On the other hand, a new and striking feature comes into prominence, /. e.. the silvery 

 color associated with pink of the larger tubercles on abdominal segments two, four, and six 

 (PI. XLIX, tig. 2b), as if the welfare of the species depended on this new eolorational feature. 

 Just how this is to be explained depends on further special observation of the living caterpillar 

 amid its surroundings of leaves and spines. 



In Eacles, stage II, a profound change takes place in the armature, the reduction of the size 

 of the spines being marked. From the prothoracic to the tenth abdominal segment they are cut 

 down, reduced. New inHuences have begun to be exerted, and the formidable set of complex 

 spines, inherited from some extinct ancestor, no longer of use. become discarded, and a new 

 kind of protection arises, these perhaps being the hairs so peculiar to this genus. In the third 

 stage the thoracic spines are as long as the body is thick, and taper at the end. which is forked; 

 in stage IV the horns are now considerably shortened, not so long as the bod}' is thick, while 

 those on the prothoracic segment are scarcely higher than bi-oad. After the tinal molt the 

 prothoracic spines (PI. XLVIIl. tigs. 3, 4) are reduced to broad, low, flattened rough tubercles; 

 those of the two following segments are reduced to short, stout, conical tubercles, about half as 

 long as those in the fourth stage, and they are now shorter than in any other genus excepting 

 Syssphinx. 



In the second stage of C. regalis the bulb of all the horns have become moditied into two 

 simple branching spines, each ending in a simple seta (PI. LIV). The larva in this stage bears a 

 forest of twelve spinulated. long, slender spines, the longer ones ecjualing half the length of the 

 bodv, while at the end of the l)ody is a less dense forest or thicket of repellant branching thornv 

 spines. 



In the third stage the horns are still slender, and the spinules, being large and long, thev 

 appear to be much branched. In the fourth stage they have become three times as stout as 

 before and of the same thickness and length, but a little longer in proportion than in the last 

 stage. Their effect is in the two last stages heightened by the black thoracic and the abdominal 

 oblique bands. 



It still remains to be seen whether these spines secrete at their base a poison; and it is to be 

 hoped that close and repeated observations will be made on the larv» while feeding to see how 

 far the}- are protected by their armature and dark conspicuous stripes from the observations of 

 birds, etc. 



It should be noted that while C. regalis has the longest spines of any species of the genus, in 

 C. scpiilcraUs the}' are shorter, while in the Brazilian C. 2)endopi- they are scarcely longer than 

 in Eacles tmperalis. 



The hairs of Eacles vs. the reduction in the spines. — The bodies of all the Ceratocampinaj 

 except Eacles are destitute of hairs. In Eacles the long irregular hairs are a generic feature. 

 They tirst appear in stage II, but in stage IV these long white hairs are fi"equently as long or a 

 little longer than the body is thick. They are longer in the penultimate than the last stage, and 

 form a more dense clothing. Now, it is well known that liirds and ichneumon flies of various 

 kinds avoid hairy caterpillars, and the question arises whether the hairs of Eacles in its last stage 

 do not to some extent protect the creature from its natural enemies, and whether, since it is thus 

 protected, the spines have undergone reduction from being no longer useful in defense. On the 

 other hand, it is only fair to state that Citheronia penelope, with horns scarcely longer than 

 those of Eacles. is destitute of long hairs, though the vestigial dorsal tubercles of the abdominal 

 segments are represented by Burmeister as giving rise each to three or four short setaj. 



The dorsal spines of Animta. — In this genus the armature is so reduced that there is but a 

 single pair of horns on a single segment, the second thoracic, and this reduction is associated in 

 the moths with the atrophy of the maxilla?. In each of the four species whose ontogeny is 

 Vol. 9— 0.T 2 



