370 THE DESCENT OF MAN. 



exception to the rule that all caterpillars of nocturnal and 

 retiring habits with smooth skins, all of a green color and 

 all which imitate twigs are greedily devoured by his birds. 

 The hairy and spinose kinds are invariably rejected, as 

 were four conspicuously colored species. When the birds 

 rejected a caterpiller the^ plainly showed by shaking their 

 heads and cleansing their beaks that they were disgusted 

 by the taste.* Three conspicuous kinds of caterpillars and 

 moths were also given to some lizards and frogs by Mr. A. 

 Butler and were rejected, though other kinds were eagerly 

 eaten. Thus the probability of Mr. Wallace's view is con- 

 firmed, namely, that certain caterpillars have been made 

 conspicuous for their own good, so as to be easily recog- 

 nized by their enemies, on nearly the same principle that 

 poisons are sold in colored bottles by druggists for the good 

 of man. We cannot, however, at present thus explain the 

 elegant diversity in the colors of many caterpillars; but 

 any species which had at some former period acquired a 

 dull, mottled or striped appearance, either in imitation of 

 surrounding objects or from the direct action of climate, 

 etc., almost certainly would not become uniform in color 

 when its tints were rendered intense and bright; for in 

 order to make a caterpiller merely conspicuous there would 

 be no selection in any definite direction. 



Summary and Concluding Remarks on Insects. Looking 

 back to the several orders we see that the sexes often diifer 

 in various charactecs, the meaning of which is not in the 

 least understood. UThe sexes, also, often differ in their 

 organs of sense and means of locomotion, so that the males 

 may quickly discover and reach the females. They differ 

 still oftener in the males possessing diversified contrivances 

 for retaining the females when found. We are, however, 

 here concerned only in a secondary degree with sexual dif- 

 f^ences of these kinds. _j 



Lin almost all the orders the males of some species, even 

 of weak and delicate kinds, are known to be highly pug- 



*See Mr. J. Jenner Weir's paper on Insects and Insectivorous 

 Birds, in "Transact. Ent. Soc," 1869, p. 21; also Mr. Butler's paper, 

 ibid., p. 27. Mr. Riley has given analogous facts in the "Third 

 Annual Report on the Noxious Insects of Missouri," 1871, p. 148. 

 Some opposed cases are, however, given by Dr. Wallace and M. H. 

 d'Orville; see " Zoological Record," 1869, p. 349, 



