BUTTERFLIES AND BEES 29 



spending to the thorax, bear small legs ; but no wings are to 

 be seen. Unlike adult insects, the caterpillar of some species 

 bears several pairs of legs on some of the abdominal segments. 

 After reaching full growth as a caterpillar the animal goes 

 into a resting stage, in which the exoskeleton becomes very hard 

 (see c, Fig. 12). Among the moths the resting stage generally 

 includes a silky covering, or cocoon, about the exoskeleton, as 

 in the case of the silk-moth. This resting stage may last from a 

 few weeks to several months, according to the species. Among 

 many species in temperate regions it lasts over the winter. The 

 pupa, whether in a cocoon or naked, appears to be perfectly life- 

 less, but we know that great changes are taking place inside. 

 When these changes are completed, the pupa breaks open, and 

 out crawls the fully formed butterfly adult, or imago. 



24. Metamorphosis. The great differences in appearance and 

 structure between the adult butterfly and each of the other stages 

 through which it passes in the course of its life history (egg, 

 larva, pupa, imago) have long aroused the wonder of observers. 

 The succession of changes from one stage to the next is called 

 metamorphosis, which means the same as transformation, that 

 is, a changing over from one form to another. ^letamorphosis in 

 development is found among many kinds of insects, but not among 

 all. The development of the grasshopper is said to show an in- 

 complete metamorphosis, since at each stage the change is not 

 so great as that observed among butterflies. Metamorphosis in 

 development is found also among higher animals, such as the newt 

 and the frog, although in these cases the stages do not correspond 

 exactly to the four stages in the butterfly's life (see section 227). 



25. The bee (Apis mellifera, honeybee; or Bombus sp., 

 bumblebee). Insects of the order represented by the honeybee 

 and the bumblebee differ in many ways from both the grass- 

 hopper and the butterfly. We see again the same general plan 

 of body, consisting of head, thorax, and abdomen ; the same 

 number and arrangement of legs and wings ; the same type of 

 food-getting and sensory organs. Moreover, there is a segmen- 

 tation of the thorax and of the abdomen, and there are spiracles 



