METAZOA INSECTA. 425 



ble larva of the two-year cicada (PL 1062). The resem- 

 blance is seen especially in the similarity of the thoracic 

 segments. 



At the time of hatching, the fore legs are fitted for 

 burrowing (PI. 1057, fig. i), having strong digging claws 

 at their ends. These are needed when the larvae, which 

 hatch from eggs laid in the branches of trees, drop to the 

 ground and begin to burrow downward to the roots. 

 Development is so extremely slow that in six years the 

 larva of the seventeen-year species has hardly attained 

 one fourth its full size (Riley). There are probably 

 twenty-five or thirty moults, the body gradually short- 

 ening, thickening, and growing darker with age. 



The larva lives on the sap of roots and the moisture in 

 the earth, which it takes by means of its strong sucking 

 tube. Much of the time it lies in an oval cell which it 

 has made for itself by using its claw as one would use a 

 pick. It never passes into a quiescent pupal stage in 

 which structural changes are gone through quickly ; 

 nevertheless, it lies in a cell, as we have said, and is able 

 to live a considerable time without taking nourishment. 

 In these ways it approaches pretty closely to the quies- 

 cent condition of the more specialized insects. Gradu- 

 ally wing pads are developed and the pupa (PI. 1057, 

 fig. 2) works its way to the surface. "To witness these 

 pupae in .... vast numbers .... swarming out of their 

 subterranean holes and scrambling over the ground, all 

 converging to the one central point, and then in a steady 

 stream clambering up the trunk and diverging again on 

 the branches, is an experience not readily forgotten and 

 affording good food for speculation on the nature of 

 instinct. The phenomenon is most satisfactorily wit- 

 nessed where there is a solitary or isolated tree." * In 

 about an hour after rising and settling, the transformation 



1 Riley, Rep. of the Entomologist, U. S. Dep. Agric., 1885, p. 

 237- 



