MEMOIRS OF 'THE NATIONAL ACADEJIY OK SCIENCES. 15 



Orif/in of the lines. — As Wei.smaiiii lias sliowii, tbe piimitive markings of caterpillars were 

 lines and lonpjitudiual bands, the sjiots appearing from interru])tions or wliat may be called tbe 

 serial atrophy of the lines or bands. It is not ditlicult to account for the origin of the dorsal line, 

 as this would naturally be due to the i)reseuce of the heart underneath. This dorsal line is, for 

 exami)le, wanting iu the freshly hatched larv.T of Sj)Hosoma rir<jinica and JIj/t>hantria iextor, but 

 after the first molt of »S'. virf/inica there is a slight, diffuse dorsal line of no decided color, though 

 after the second ccdysis it is decidedly whitish, or at least much jialer than the surrounding dorsal 

 region. In pale caterjullars the dorsal line may be darker. In the first stages of the two moths 

 iu question there are no lines or bands; only the xnliferous warts. Whether the subdorsal or the 

 spiracular lines were the tirst to originate is uncertain, hut probably, from what Weismann has 

 concluded fi-om his studies of the Sphingida', the subdorsal arose tirst. In the second stage of 

 Spilosoma virginica the subdorsal lines are reddish lines extending between the two subdorsal 

 rows of alternating subdorsal piliferous warts, the line becoming more decided, however, in the 

 third stage of this species, there being as yet no signs of a spiracular or of any lateral line. In 

 the freshly hatched larva of H. textor, however, what may be the first beginnings of the subdorsal 

 line are elongated brownish linear spots inclosing the subdorsal row of larger piliferous dots, but 

 not reaching the sutures between the segments. These patches, however, do not in the second 

 stage unite to form continuous lines, but two rows of decided black elongated spots inclosing 

 the black piliferous tubercles. In the freshly hatched larva of Edema albi/rons each of the two 

 subdorsal lines is a row of elongated black spots connected on the three thoracic segments, but 

 separated by the sutures along the abdominal segments. 



The spiracular line is seen in the same larva of the same stage to be a yellowish band inclosing 

 the spiracles, and there seems to be a tendency in some, if not many, larvie for the spiracles to be 

 inclosed and connected by a parti-colored or bright line, and for this to have a darker (as in Edema) 

 or lighter edging. Why the spiracles themselves are so apt, as in Bombyces and Sphinges, to be 

 inclosed by a dark or conspicuous line remains to be explained. 



To return to the subdorsal lines in the pale reddish larva of Datana, probably J>. inleyerrima, 

 these lines before the tirst molt are also inclosed by the two rows of subdorsal piliferous spots, 

 and in both the first and second stages there are pale spiracular lines, which appear to be contem- 

 iioraneous with the subdorsal line. In the third stage a new dark red line is interpolated between 

 the subdorsal and spiracular. In the fourth stage the spiracular hue has disappeared, and there 

 is a supra and an infra- spiracular pale line on the now brown, dark skin of the caterijillar. Seen 

 from above there are four pale lilac lines, but after molting two of them disappear, and in the 

 last stage there are only two subdorsal lines to be seen, if my colored drawings, very carefully 

 made by Mr. Brigham, are correct. We thus see that after the subdorsal and spiracular lines are 

 formed, others are rapidly introduced — and some may as rapidly vanish, as necessary features of 

 certain stages — which, when they become useless are discarded. 



The admirable and most suggestive work of Weismann has placed on a sound basis the theory 

 of the origin of the lines, bands, and spots of the Sphingidic. The additional notes by Professor 

 Meldola and the beautiful researches of Mr. Poultou have added to the strength of the arguments 

 of Weismann. The lines, bars, stripes, spots, and other colorational markings of caterpillars, by 

 which they mimic the colors and shadows of leaves, stems, etc., have evidently been iu the tirst place 

 induced by the nature of the food (chlorophyll), by the effects produced by light and shade, by 

 adaptation to the form of the edge of the leaf, as in the serrated back of certain Notodontians, by 

 adaptation to the colors of different leaves and to the stems, often reddish, shades of greens, yellows, 

 reds, and browns being as common iu the cuticle of caterpillars as on the surface or cuticle of the 

 leaves and their stems or in the bark of the twigs and branches. We (and probably others) have 

 observed that the peculiar brown spots and patches of certain Notodontians do not appear until 

 late iu larval life, and also late in the summer or early iu the autumn contemporaneous with the 

 appearance of dead and sere blotches in the leaves themselves. 



Now, to say that these wonderful adaptations and marked changes iu the markings of cater 

 ])illars are due to ''natural selection," and to let the matter rest there, is quite unsatisfactory. 

 Natural selection may account for the elaboration of these larval forms with their markings after 

 they have once appeared, but we want to discover, if possible, the original causes of such orna- 



