MEMOIRS OF THE NATIONAL ACADE.MY OF SCIENCES. 17 



1, 3. (s-l). In stage III, the pruportion between the .spines is .still the same; now, small .sec- 

 ondary sctiferous tubercles have arisen. In stage V (tig. 6) the two lateral tubercles .s7 are 

 reduced to low flattened four-headed ones, and the plate is well rounded at the end; the two 

 terminal black tubercles are minute, while the surface of the plate is without secondary tubercles, 

 not being coarsely granulated as it is in Eacles. In C. sjj/e/xh/i.s (PI. LV, tig. 1«, 1/^) the arma- 

 ture is more excessively developed than in C. regali-^ or any species of the genus, and the surface 

 of the plate is covered with transverse rows of secondary tubercles, the two terminal tubercles 

 being distinct. In C. scj^idcmh'x the armature of the surface is intermediate between the two 

 species named (figs, -ia, ih), while in C. laocomi the plate is nearly smooth, with small tubercles 

 .vi, being much as iu C. rcgalls. On the other hand, in C. phui-onea^ judging by Burmeister's 

 figure, tubercles si are much longer, but the surface is merely rugose as in C re(ial!». 



In conclusion, the suranal plate and its armatui-e coincide or are congruent with the other 

 larval characters, .so that if found fossil they would afl'ord a fair basis for identification and 

 classification. 



III. THE CAUDAL HORN OF THE CERATOCAMPIDiE. 



The larvif of Ceratocampida^ and .Saturniidai, as well as a few other lepidopterous larva> of 

 other groups, and more especially the Sphingida?. are characterized by possessing the so-called 

 •"caudal horn." This modified tubercle is now known to be the result of the fusion either before 

 birth, or before the first ecdysis, of the dorsal tubercles / of the two anterior tubercles of the 

 eighth abdominal segment. We have designated this double tubercle as the "eighth uromeral 

 tubercle;" the term uromere being applied to any one of the abdominal segments. We will first 

 describe it in the group Ceratocampinti?, and then discuss its mode of origin and occurrence, as 

 well as its phylogenetic significance, in other groups. 



Caudal horn of Cfndoatmpiniv. — In the species of the most generalized genus. Adclocephala, 

 the caudal horn is very large and prominent, as long as any of the thoracic horns in A. hlcolor, 

 twice as thick, and considerably stouter; it is roughly tuberculated with secondarv setiferous 

 tubercles; and at the tip has lost the bifid nature of the first two stages, ending in a single 

 tubercle which does not bear a terminal seta. 



We will now trace its history from stage I up to the last. The great thick club-like slightly 

 curved horn ends in two primary tubercles, each bearing a stifl' seta about as long as these 

 tubercles (PI. XLV, fig. 1). In stage II (tig. 3), the caudal horn is slenderer than before (in the 

 .specimen figured it had become flattened down and attached flrmly along the back). 



In the third and fourth stages the bitid nature is lost, and the horn ends in a single 

 bristleless tu>)ercle as in the last stage, the terminal or primary tubercle being but little larger 

 than the secondary ones which render the horn so rough and coar.sely spinose. 



In the full-grown larva? of ^4. autrdl and ai-gyracantha, as flgured by Burmei.stei', the caudal 

 horn is slightly longer and twice as thick as either of the thoracic ones. 



In stage I of %.«.y/>7/ //;,?• nioJina the caudal horn, like that of Adclocephala. is entirdv unlike 

 in .shape and length the thoracic horns, being much shorter and nearly twice as tliick (PI. XLVIl). 

 In Sy.ssphinx the swollen, squarish end bears on each side a short rounded tubercle, each givino- 

 rise to a long bri.stle. the main tubercle showing no signs of its double origin. 



In EacJcs inqHrialix the caudal hoi-n is nearly as large as any of the thoracic ones of the 

 same shape, the end being deeply divided, with no deflnite line of division between the two 

 terminal tubercles and the main shaft of the "horn;" the seta? are a little longer than the forks 

 or branches. After the flr.st molt the proportions are the siimc. all the horns being reduced in 

 .size. In .stage III the horn is si ill |,,i,g and slender, but unly aliout one-lialf as long as the 

 longest thoracii- horns. 



After the third ecdysis there is a decided reduction in size of the caudal horn, which, though 

 still quite large and prominent, is ordy al)out half as long and large as the largest thoracic horns. 

 In the fully grown larva?, where the process of reduction has aflected all the armature, especial Iv 

 the dorsal spines, the caudal horn is reduced to a conical spinose tubercle but little higher than 

 broad, though still only about half as high as the larger thoracic ones; and now the somewhat 

 dense secondarj- hairs rise far above the dorsal spines. 



