on colour-relation. 248 



ncath, with the hght shining through them, the loaf-spots 

 were of a red exactly corresponding to that of the larva- 

 spots, and much the same size. I did not, however, see 

 the likeness to qalls {PJujtoptus) suggested by Mr. 

 Cameron (Trans. Ent. Soc! 1880, p. 69), for the effect 

 produced by a flat spot and a raised object such as a 

 gall would, I think, be very different. But my larva was 

 quite difficult to find, even on a small twig, when viewed 

 from below, and it would have been admirably concealed 

 from enemies below it at any rate. 



In S. tilice I could see nothing in the spots which 

 would have led me to connect them with coloured bor- 

 ders until the second larva reached its last stage, but the 

 appearance of the spots in this individual was so linear 

 and so unmistakeably border-like, that it seemed im- 

 possible to doubt the correspondence. 



It would have been natural to conclude, from appear- 

 ances, that the spots are merely protective in S. 'populi, 

 and in S. tilice have either degenerated from coloured bor- 

 ders, or are on the way to become such ; but that it seems 

 unlikely that the character can have a diflerent signifi- 

 cance in the two species. It seems to me more probable 

 that spot-marking is the most ancestral, as Prof. Weis- 

 mann originally suggested, and that S. tilice represents 

 a stage of its modification into stripes. The fact that 

 the spots do increase in area in both species, though in 

 two directions, seems to point to the character being a 

 developing one. If we had to do with a gradual short- 

 ening of borders contracting into spot-markings, it seems 

 more likely that if any change in area of the spots took 

 place it would be in the direction of contraction, which 

 was never the case in my larvae. There seemed to be 

 no vestige of a former extension along the stripe ; even 

 when a stripe was suffused with red, it was so vertically 

 downwards, and never partially affected an extra ring so 

 as to lead one to suppose the spot had once been broader. 

 But the number of larvte reared was too limited to draw 

 conclusions from safely, and it is possible that if I had 

 had more individuals under observation, some of them 

 might have presented different appearances. 



4. Experiments as to the palatability of conspicuous lame. 



In May and June, 1890, I made experiments with 



larvee of Diloha ccerideocephala and CucuUia verbasci on a 



