372 Studies in the Theory of Descent. 



to which dorsal and spiracular lines may have 

 been added. That this second stage of phyletic 

 development has also been preserved in existing 

 species has already been sufficiently shown ; the 

 greater portion of one group, the Macroglos since, 

 has indeed remained at this stage of develop- 

 ment. 



From the biological value which must be attri- 

 buted to this kind of marking, its origination by 

 natural selection presents no difficulty. The first 

 rudiments of striping must have been useful, since 

 they must have broken up the large surface of the 

 body of the caterpillar into several portions, and 

 would thus have rendered it less conspicuous to its 

 enemies. 



Thus it is not difficult to perceive how a whole 

 group of genera could have made shift with this 

 low grade of marking up to the present time. 

 Colour and marking are not the only means of 

 offence and defence possessed by these insects ; and 

 it is just such simply-marked larvae as those of the 

 Macroglossincz which have the protective habit of 

 feeding only at night, and of concealing themselves 

 by day. Moreover, under certain conditions of 

 life the longitudinal stripes may be a better means 

 of protection, even for a Sphinx-larva, than any 

 other marking ; and all those species in which this 

 pattern is retained at the present time live either 

 among grasses or on Conifers. 



It cannot be properly said that the second form 



