XIX] LIFE HISTORY 359 



The larva escapes by splitting the egg membrane at the broad 

 end of the groove. During August, with an average tempera- 

 ture of 72 F. in the day and 65 at night, the incubation 

 period varies from two to three days. 



The young larva is round, smooth, and almost transparent, 

 and of the usual acephalous muscid type (Fig. 6, p. 20). It 

 may be distinguished by the appearance of the two posterior 

 stigmata, which are small, circular and situated rather far apart. 

 Its length when full grown is about n mm. The duration of 



Fig. 84. Stomoxys calcitvans. Eggs. The small group in the top left hand 

 corner represents their natural size. (After Newstead.) 



the larval stage under favourable conditions, is from two to 

 three weeks, but the absence of plentiful moisture or exposure 

 to light retards the development very considerably, to at least 

 a period of 78 days. Such larvae produce abnormally small 

 pupae and correspondingly small adults. 



The process of pupation is completed within two hours. 

 The larva first burrows to some little depth and then shortens 

 itself by contraction of the front segments, thus becoming 

 barrel-shaped (Fig. 9, p. 22). The colour of the pupae is at 

 first terra-cotta, but it subsequently darkens to a chestnut- 



