THE CA TERPILLAR. . 27 



cle of the seventh segment exudes a sweetened 

 fluid, very grateful to ants, and the spiny -crowned 

 tentacles on the next segment serve, when erected, 

 as indications to the ants that the feast is ready. 

 The ants in their turn act as guards to keep off the 

 attack of Ichneumon enemies from their willing 

 hosts, and thus each serves the other a good turn. 



These are all the external parts of a caterpillar 

 which it is now necessary to consider. But there 

 is one peculiarity of its growth, which, though 

 very curious, has been but little noticed, and 

 only recently has been shown to be of probably 

 universal application. When any one character- 

 istic is found throughout an entire group we nat- 

 urally inquire what its meaning may be ; espe- 

 cially in these days when evolution is required to 

 explain everything or nothing. In this place, I 

 shall only present the facts, and leave a possible 

 explanation for a later chapter. 



Every caterpillar in its growth from the egg to 

 maturity changes the character of its coating. I 

 do not refer to that periodic sloughing of the in- 

 tegument common to the early stages of all in- 

 sects, the reason for which is quite apparent, 

 since otherwise their inelastic coats would be too 

 strait for their rapidly growing bodies. But I 

 call attention rather to the fact that with the first 

 sloughing of the integument an entirely different 

 set of appendages is assumed. The fresh integu- 



