Packaud.] 



INSECTS AS ARCHITECTS. 



305 



the ground, with a hole (e) at the base. Mr. Rathvon, 

 who observed this fact, says that the pupae await in the 

 upper end of these chambers their time of transformation 

 into the wiiii^ed state, and wlien about to come from the 

 ground, move backwards down the tube to below the level 

 of the earth as at d, " and issuing forth from the orifice 

 would attach themselves to the first object at hand, and 

 undergo their transformations in the usual manner." 



Many plant lice allied to the Aphis, by their punctures 

 cause the adjacent parts of the leaf to curl over and conceal 



Fig 



Younpr 17-vcar Cio.aila and its nest. 



them, or even give rise to the true galls, as elaborate as 

 those of the gull lly. A kind of Peniijhigus forms on the 

 sumac the irregular growth represented by figure 23G (after 

 Riley). The cock's-comb elm gall (Fig. 237, after Riley) 

 often occurs in great numbers on the leaves of the white elm. 

 "By the end of June or the beginning," says JMr. Walsh, 

 "the gall becomes full of winged plant-lice, when the slit on 

 the upper side of the leaf, through which the mother plant- 

 louse built up the gall early in tlie spring, gapes open and 

 20 17 



