124 REPRODUCTION 



Between these points of sudden change there are periods 

 during which there is little or no change but growth. 



Some of the most beautiful illustrations of metamor- 

 phosis in the growing up of offspring are found in the 

 insects. Very many of the insects undergo a profound and 

 striking metamorphosis. In the moths and butterflies we 

 have a story something like this: 



(1) There is considerable food in the egg, and when 

 it hatches the animal that comes out is a small 

 worm-like object which we call a caterpillar 

 (larva). 



(2) This feeds on leaves and the like and grows, but 

 remains a caterpillar for weeks or months, during 

 which time it stores up a large quantity of food. 



(3) At the close of this period the caterpillar becomes 

 quiet and inactive, often secreting about itself a 

 protecting case. 



(4) In this cocoon the whole structure is gradually 

 but profoundly changed within, though there is no 

 difference in the outside appearance of the cocoon. 

 Old organs are taken up by the blood and new 

 ones, suitable to the mature life, are developed 

 from the stored-up material. Wings, of which 

 there was no trace in the larva, long legs instead 

 of the poor, stumpy ones, and different eyes and 

 mouth parts appear. 



(5) When this has all happened the changed animal 

 breaks from the cocoon in the adult form of the 

 butterfly. In this form it reproduces by eggs and 

 sperms, and mating takes place. Thus the cycle 

 is complete. 



6. Possible Advantages in Metamorphosis. Without 

 doubt this round-about development has both its 

 advantages and disadvantages to the species, but on the 

 whole it looks as though it aids the process of successful 

 reproduction more than it hurts it. The adult butterflies 



