( cxxxii ) 



Marshall on the marked difference in habit of the seasonal 

 forms of Precis sesamus and octavia-natalensis, and those of Dr. 

 Chapman, Commander J. J. Walker, and Mr. Tutt, in their 

 numerous writings, add much to our conceptions of insect life, 

 and similar observations of the same nature can hardly fail to 

 throw light on some of the problems which that life presents, 

 including those of structure, with which habits and functions 

 are so closely allied. 



Relations between habits and strvctnre. 



Special habits may derive much importance from this close 

 connection with structure. It is of no protective use for a 

 moth to be whitish grey if its habit is to rest on a dark brown 

 tree trunk or indiscriminately on objects of any colour, but its 

 colour may be of the greatest use if its habit is to rest on light 

 grey stones. It may be urged that it is the structure which 

 dictates the habit. So it does in the main ; an Anthrocerid 

 cannot hover like a hawk moth, or soar and glide like an 

 Apatvirid. But when structure was in the making, the habits, 

 taken in connection with natural selection, must have bad much 

 to do with that making, and, so far as structure is being now 

 made, present habits must have much to do with future shaping. 



At the same time, the importance of habits (or even of 



facies) must not be exaggerated. The former are necessarily 



less rigid and more easily adaptable to temporai-y surroundings 



than structure can be. Coloui', as shown by experiments 



(including my own), can in individuals be altered by moderate 



differences in temperature, well within the compass of what they 



would encounter under natural conditions, directly applied in 



the pupal stage, and seasonal forms often show immense 



differences not only in colour, but in pattern, shape, and size. 



In some local or seasonal for-ms the difference in facies, in 



others the difference in habits, seems to be the greater.* 



* Some laivte of Cucidlia lucifuga, of which I took a few near Dissentis 

 early one September, atforded a remarkable example of community of 

 habits in two diti'erent stages presenting a vast divergence in appearance. 

 The}' lay about motionless, but, if touched, ran away at racing speed. They 

 were of a light chocolate colour with several conspicuous bright yellow 

 longitudinal stripes. When I opened the box a day or two afterwarels 1 

 found three sooty black larvte with rows of small deep orange spots. They 

 were so dissimilar to what I had found tliat I thought 1 must have made 

 some mistake. But their liabits showed at once what they were. When 

 one was touched it rushed about at amazing speed (" vera incessu patuit "). 



