THE BIOGENETIC LAW 177 



in the spirally coiled shell in the course of ages appeared first on the 

 last whorl, and then subsequently extended to the one before this, 

 and thence to the still younger whorls of the shell. Meanwhile the 

 last whorl not infrequently exhibited another new character. Thus, 

 for instance, protuberances on the shell were shifted in the course 

 of the phylogeny from the last convolution to the second last, and 

 later to the third last, and so on, while at the same time the last 

 convolution showed the protuberance changed into spines. In other 

 words, the new phyletic acquirements first aj)peared in the mature 

 animal (in the last-formed whorl or chamber of the shell), but were 

 subsequently shifted back in the ontogeny to younger stages in 

 proportion as new transformations of the mature animal appeared. 

 Thus there was, so to speak, a retraction of the phyletic acquisitions 

 of the mature animal deeper and deeper into the germinal history 

 of the species. 



About the same time — in the seventies — I obtained similar 

 results from living species when I was attempting to work out the 

 ontogeny of the markings on the external skin of the caterpillars 

 of certain butterflies, and I should like to submit a short account 

 of these. 



In one of the early lectures we discussed the protective and 

 defensive colours of caterpillars in general, and those of caterpillars 

 of the Sphingidai in particular. I showed that those naked cater- 

 pillars which live on plants among the grass, or on the grass itself, 

 are often not only green, like fresh grciss-stalks, or yellowish-grey, 

 like dry ones, but all the larger forms also exhibit light, usually 

 white, longitudinal lines, which, by mimicking the sharp light refl.ec- 

 tions on the grass-stems, heighten the protective resemblance. 



We also spoke of the light transverse stripes, often marked with 

 pink or lilac-blue, of many of the large green caterpillars which live 

 on trees and bushes, and whose likeness to the leaves is heightened 

 by this imitation of the lateral veining of a leaf ; and finally we 

 mentioned the warning coloration indicative of unpleasant or nauseous 

 taste, among which must be classed not only vivid contrasts of colour, 

 but also specially conspicuous elements of colour such as light ring- 

 spots upon a dark ground. These different colour schemes which 

 protect the caterpillars from their enemies are usually only to be 

 found in the adolescent caterpillar, not in the very small one which 

 has just emerged from the egg, and the development of the markings 

 in the individual life clearly shows that the phylogeny of the mark- 

 ings is more or less obviously contained in the ontogeny. 



There are three different schemes of markino- which occur in the 



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II. N 



