The Origin of the Markings of Caterpillars. 289 



IV. 



BIOLOGICAL VALUE OF COLOUR. 



THE general prevalence of protective colouring 

 among caterpillars has already been so frequently 

 treated of that it is not here my intention to 

 recall particular instances. In order to judge of 

 the effect of marking, however, it will be well to 

 bear in mind that these insects, being generally 

 defenceless and thus requiring protection, have 

 acquired the most diverse means of rendering 

 themselves in some measure secure from their 

 foes. 



The sharp spines which occur on the cater- 

 pillars of many butterflies (Vanessa, Melitcea, 

 Argynnis), and the hairs on those of many moths, 

 serve for protective purposes. Among other 

 means of protection although in a different sense 

 we have in all the species of the great family of 

 the Papiliomda the strikingly coloured (yellowish 

 red) odour-emitting tentacles concealed near the 

 head, and suddenly protruded for terrifying foes ; 

 and likewise the forked horn at the tail of the 

 caterpillars of the genus of moths Harpy ia, the 



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