THE MARGUERITE FLY. 43 



about by the contraction of the anteriorniost ventral larval segments before 

 the larva becomes inactive, drawing along with it, first upward then 

 analward, the anterior dorsal portion of the body. As a consequence, the 

 cephahc spiracles, which in the larva are situated on the posterior portion 

 of the second dorsal segment, assume an anterior ventral position in the 

 puparium. 



In shape the puparium may be said to be scaphiform or boat-shaped. 

 In outhne it is long oval, and approximates in a general way towards that 

 of the larva, being broadest anterior to the center, and tapering from its 

 stoutest portion anteriorly and posteriorly, terminating acutelj' anteriorly 

 and somewhat truncately posteriorly. As a rule, the length is twace the 

 width (width across the stoutest portion), although not infrequently the 

 width exceeds half the length. A large number of measurements showed 

 a length of 2.25 to 3 millimeters and a width of 1 milhmeter to 1.5 milli- 

 meters. The greatest width does not necessarily go with the greatest 

 length. The segments are quite strongly marked, and the spiracles are 

 prominent. 



While the puparia are seen through the epidermis (Fig. 11) on either 

 surface of the leaf, by far the greater number occur near the lower surface, 

 the proportion being about 2:1; that is to say, pupation takes place more 

 often immediately above the epidermis of the lower surface of the leaf than 

 immediately below the epidermis of the upper surface, the larvse when 

 about full grown making their way towards the lower surface for that 

 purpose by eating their way through the central portion of the mesophyl. 

 The mining is continued, as a rule, for a greater or lesser distance, after 

 they have eaten their way through. 



The puparial content, at first a semiUquid, wliitish mass which chngs 

 to the wall of the puparium, gradually hardens, thi-ough the loss of its 

 fluids, into a white mass distinct from the puparial wall. This mass then 

 gradually differentiates into the pupa proper, which shows the three 

 primary regions — head, thorax and abdomen — of the adult insect, and 

 the rudimentary legs and wings or wing buds. The pupa proper is formed 

 witliin two and one-half days after pupation at a temperature of about 

 60° at night and 70° and over during the day, — temperatures sUghtly 

 liigher than those at which marguerites and low-temperature loving plants 

 of its kind are usually kept. It is quite probable that at those lower tem- 

 peratures the results would be shghtly modified. The pupa proper is 

 cream- white in color; the legs are folded on the ventral surface; the -wing 

 buds are pressed closely to the sides of the body, their apical portions 

 inclining ventrally. 



Length of Pupal Life. 



The length of the pupal period, like that of the egg and larva, varies 

 with the temperature, as will be seen by the tables that follow. In all, 

 the periods of 197 are available. One hundred and thirty-four of these 

 developed in plants in the insectary during November, and were subjected 

 to a temperature similar to that to which the eggs and larvae were sub- 



