32 



PRINCIPLES OF ANIMAL BIOLOGY 



iterpillar or grub or maggot, from which a person ignorant of the Hfe 

 istory could not possibly predict the adult (see Fig. 186). After growth, 

 lese larvae become quiescent pupcB, enclosing themselves in a chitinous 

 ise and taking no food. They may undergo squirming movements, but 

 re incapable of locomotion. However, in some of them remarkable 

 langes are going on in the interior during this quiescent period. Many 

 ; the cells of the larva disappear entirely, being dissolved and devoured 

 y certain wandering cells. Whole organs may appear thus to degene- 

 ite into a milky pulpy mass. But some cells always remain, and out of 

 lese the organs of the adult take their origin. Doubtless the material 

 erived from the degeneration of the lost organs is used as nutrition for 



iG. 186. — Metamorphosis of the swale-fly Sepedon fuscipennis. A, larva; B, pupa; C, 

 adult from above; D, adult, side view. (From Needham.) 



le development of the adult organs, but there is much uncertainty as 

 ) just what happens during that process. This destruction of the larval 

 [■gans, and the formation of new organs out of their remains, constitutes 

 )r these insects the process of metamorphosis. 



Metamorphosis in Vertebrates. — In some of the higher groups, 

 letamorphosis, where it occurs at all, is shrouded in much less mystery, 

 n the vertebrates, the transformation of a tadpole into a frog or toad is 

 le classical example. The readily visible changes are the degeneration 

 f the so-called "sucker," or attaching organ, beneath the head; the de- 

 elopment of the legs; and the absorption of the tail, the material of 

 'hich is probably used elsewhere for growth. Besides these changes 



