264 



CHAPTERS ON EVOLUTION. 



FIG. 175. GRASSHOPPER. 



slowly and gradually, would in time become naturally repeated in the 

 life-history of the race. Or, further, as Sir John Lubbock suggests, 

 the young insect might have access to, or even be compelled to eat, 

 different kinds of food at different periods of its existence. Every 

 variation of mouth has a reference, like the form of larva, to the life 

 and food of its possessor. Is there, after all, any great difficulty in 



conceiving that the varying 

 forces and conditions which 

 include in their work the 

 production of very different 

 larvae in even a single group 

 of insects, should have like- 

 wise altered and transformed 

 the mouth-parts of these ani- 

 mals ? In truth, alteration of 

 mouth is simply a part of a 

 transformation which becomes 

 the more wonderful as our 

 view of its scope enlarges. Nor does the consideration of the origin 

 of the insect mouth fail to lead us incidentally to discuss the meaning 

 of the pupa or chrysalis stage. " Granting, then," says Sir John 



,. -i | > >, Lubbock, in speaking 



L'/ . , ^ I ^ ^ 3 ^ of the modification of 



the biting to form the 

 suctorial mouth, " the 

 transition from the one 

 condition to the other, 

 this would no doubt 

 take place contempo- 

 raneously with a change 

 of skin. At such times 

 we know that, even 

 when there is no change 

 in form, the softness of 

 the organs temporarily 

 precludes the insect 

 from feeding for a time, 

 as, for instance, in the 

 case of caterpillars. 

 If, however, any con- 

 siderable change were 



evolved, this period of fasting must be prolonged, and would lead 

 to the existence of a third condition, that of the pupa, intermediate 

 between the other two. Since the acquisition of wings is a more 

 conspicuous change than any relating to the mouth, we are apt to 



FIG. 176. CRICKET. 



a, eggs ; b, arvx (natural size) ; c, magnified ; d, chrysalis ; 

 e, perfect insect. 



