908 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°—35°C., 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. Larvee incubated at a temperature 
of 35°C. 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 larvee 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 ; larve 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.—tThe 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 63 mm. Owing to the with- 
drawal of the anterior segments the antertor spiracular pro- 
cesses (a.sp.) are now situated at the anterior end, and the 
posterior spiracles (p.sp.) form two flat button-lke 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 anpeeun the larva 
loses its tracheal system, which appears to be withdrawn 
