508 C. GORDON HEWITT. 



sclerites are much deeper, thus making the dorsal and ventral 

 posterior processes more slender than in the mature larva. 

 The second larval instar may undergo ecdysis in twenty-four 

 hours at a temperature of 25 35C., but under cooler con- 

 ditions or with a deficiency of moisture the period is pro- 

 longed and may take several days. 



The third larval stage or third instar, which is the last larval 

 stage, grows rapidly. The anatomy of this the mature larva 

 will be fully described. Larvae incubated at a temperature 

 of 35C. complete this larval stage and pupate in three to 

 four days, on the other hand, under less favourable develop- 

 mental conditions, it sometimes extended over a period of 

 eight or nine days. Incubated larvae cease feeding at the end 

 of the second day of this stage and gradually assume a creamy 

 colour, which colour is due to the large development of the 

 fat body and to the histolytic changes which are taking place 

 internally ; larvae dissected at this stage contain a very large 

 amount of adipose tissue cells. Between the third and fourth 

 day the larva contracts to form the pupa. 



4. The Pupa. The process of pupation may be completed 

 in so short a time as six hours. The larva contracts, the 

 anterior end especially being drawn in, with the result that a 

 cylindrical pupal case is formed (fig. 15), the posterior region 

 being very slightly larger in diameter than the anterior; the 

 anterior and posterior extremities are evenly rounded. The 

 average length of the pupa is 6*3 mm. Owing to the with- 

 drawal of the anterior segments the anterior spiracular pro- 

 cesses (a.sp.) are now situated at the anterior end, and the 

 posterior spiracles (p.sp.) form two flat button-like promi- 

 nences on the posterior end. The pupa changes from the 

 creamy-yellow colour of the larva to a rich dark brown in a 

 few hours. As the last larval skin has formed the pupal case, 

 it being a coarctate pupa, in addition to the persistance of 

 the spiracular processes the other larval features such as 

 spiny locomotory pads can be seen. 



During the first twelve hours or so of pupation the larva 

 loses its tracheal system, which appears to be withdrawn 



