THE BIOGENETIC LAW 183 



any stage. Leaving out of the question tlie absolutely unmarked 

 little caterpillar which emerges from the egg (Fig. ii8, A), there 

 appears at once in the second stage a series of ring-spots connected 

 by a fine white sub-dorsal line (Fig. ii8, B). In the following 

 stage, the third, this sub-dorsal line disappears without leaving 

 a trace, and there remains only the spot-marking, which is subse- 

 quently duplicated. 



Let us compare with this the ontogeny of the bed-straw hawk- 

 moth, Deilephila galii (Fig. 1 1 7). The full-grown caterpillar possesses 

 only a single row of ring-spots [B), and accordingly the young 

 stages of the caterpillar up to the fourth show a distinct sub- 

 dorsal line [A], although spots are seen upon it. A still earlier 

 phyletic stage of development is illustrated by Deilepliila Uvornica, 

 in which the ring-spots are all connected by the sub- dorsal line. 



It can thus hardly be doubted that the biogenetic law is guiding 

 us aright when we conclude from a comparison of the ontogeny of 

 the different species of Deilephila, that the oldest ancestors of the 

 genus possessed only the longitudinal stripes, and that from these 

 small pieces were cut off as ring-spots, and that these were gradually 

 perfected and ultimately duplicated, while at the same time the 

 original marking, the longitudinal stripe, was shunted back further 

 and further in the young stages, until it finall}^ disappeared 

 altogether. 



Let us now refer for a moment to the third form of marking 

 in the caterpillars of the Sphingidaa — transverse striping. This has 

 not arisen out of the sub-dorsal line, but quite independently and at 

 a later date. This is proved with great certainty by the ontogeny 

 of species of the genus SmerintJms. The full-grown, and usually also 

 the young caterpillars, of these species have quite regularly the seven 

 broad oblique stripes which run in the direction of the tail-horn 

 at equal intervals on the lateral surfaces of the body (Fig. 3). 

 They are absent only from the three anterior segments, and upon 

 these a part of the older marking, the sub-dorsal stripe, has persisted. 

 But we find this fully developed in the youngest stages of other 

 species. In Smerinthus loopuli, the little caterpillar, which has no 

 markings at all when it leaves the egg, very soon shows the white 

 sub-dorsal line, and simultaneously with it the seven transverse 

 stripes, which cut obliquely through it ; in the older caterpillars the 

 sub-dorsal then disappears (Fig. 119). 



When I was investigating these matters at the beginning of the 

 seventies I did not succeed in procuring eggs of the species of the 

 genus Sphinx, which likewise almost all exhibit the oblique striping 



