The Origin of the Markings of Caterpillars. 381 



Their successors, through natural selection, be- 

 came longitudinally striped ; they acquired a sub- 

 dorsal line extending from the horn to the head, as 

 well as a spiracular, and sometimes also a dorsal, 

 line. The caterpillars thus marked must have 

 been best hidden on those plants in which an 

 arrangement of parallel linear parts predominated ; 

 and we may venture to suppose that at this period 

 most of the larvae of the Sphingidce lived on or 

 among such plants (grasses). 



At a later period oblique stripes were added to 

 the longitudinal lines, the former (almost always) 

 slanting across the seven hindmost segments from 

 the back towards the feet in the direction of the 

 caudal horn. Whether these stripes all arose 

 simultaneously, or, as is more probable, whether 

 only one at first appeared, which was then trans- 

 ferred to the other segments by correlation 

 assisted by natural selection, cannot, at least 

 from the facts available, at present be determined. 



On the whole, as the oblique stripes became 

 lengthened towards the back, the longitudinal lines 

 disappeared, since they injured the deceptive effect 

 of the stripes. In many species also there were 

 formed dark or variegated coloured edges to the 

 oblique stripes, in imitation of the shadow lines cast 

 by the leaf-ribs. 



Whilst one group toiSpkirigida (Sphinx, Smerin- 

 thus) were thus striving to 'make their external 

 appearance approximate more and more to that of 



