[164] [The question here also suggests itself as to why the _dorsal_ line should not have been the primary longitudinal stripe, seeing that such a marking is almost naturally produced in many caterpillars by the food in the alimentary canal; or, in other words, why has not natural selection taken advantage of such an obvious means of producing a stripe in cases where it would have been advantageous? In answer to this I may state, that in large numbers of species the dorsal line has thus become utilized; but in the case of large caterpillars resting among foliage, it can be easily seen that light lateral (_i.e._ subdorsal) stripes, are more effective in breaking the homogeneity of the body than a dorsal line only slightly darker than the general ground-colour. Lateral lines are in fact visible from _two directions of space_. If a caterpillar thus marked be placed on a twig, these lines are visible when we look at the creature’s back or at either side. That the subdorsal are therefore the primary lines, as shown by Dr. Weismann’s observations of the ontogeny of many of the _Sphingidæ_, is quite in harmony with the view of their having been produced by natural selection. R.M.] [165] “Die Darwin’sche Theorie. Elf Vorlesungen über die Entstehung der Thiere und Pflanzen durch Naturzüchtung.” 2nd ed., Leipzig, 1875, p. 195. [166] [In the following species, already mentioned in previous notes, the oblique stripes are bounded at their upper extremities by a conspicuous subdorsal line:--_Acosmeryx Anceus_, Cram.; _Sphinx Cingulata_, Fabr.; _Pachylia Ficus_, Linn.; _P. Syces_, Hübn. In _Pseudosphinx Cyrtolophia_, Butl., the oblique white stripes, beautifully shaded with pink, run into the white pink-bordered dorsal line, so that when seen from above the markings present the appearance of the midrib and lateral veins of a leaf, and are probably specially adapted for this purpose. R.M.] [167] [The dorsal line as well as the oblique stripes is present in the caterpillar of _Smerinthus Tartarinovii_, Ménét.; and in _Ambulyx Gannascus_, Stoll., the oblique stripes are bounded above by a subdorsal line, as in the species named in the preceding note. R.M.] [168] Cat. Lep. East India Co., Pl. XI. [169] [Compare this with Darwin’s “Origin of Species” (1st. ed. p. 440), where it is stated that when an animal, during any part of its embryonic career, is active, and has to provide for itself, “the period of activity may come on earlier or later in life; but whenever it comes on, the adaptation of the larva to its conditions of life is just as perfect and beautiful as in the adult animal. From such special adaptations the similarity of the larvæ or active embryos of allied animals is sometimes much obscured.” R.M.] [170] [For Fritz Müller’s application of this principle to the case of certain groups of Brazilian butterflies see Appendix II. to this Part. R.M.] Transcriber’s Notes