46 LIFE-HISTORY 



withdrawal of the anterior segments, and assumes a cylindrical 

 shape, the ends being evenly rounded. The larva now retracts from 

 the outer skin, which remains outside as the barrel-shaped pupa- 

 rium, and its organs after undergoing disintegration are built 

 up into those of the future fly. Within twenty-four hours most 

 of the parts of the future fly can be distinguished although 

 sheathed in a protecting nymphal membrane. The pupa, or 

 more properly the puparium, is at first of a pale yellow colour, 

 but rapidly changes to bright red and finally to a dark chestnut 

 colour. It is barrel-shaped, the posterior portion being slightly 

 larger in diameter than the anterior, and both ends equally 

 rounded. At the posterior end are two minute processes corre- 

 sponding to the larval spiracles and " the locomotory pads can 

 still be recognized as roughened areas on the ventral side of the 

 pupa" (Hewitt, 1912, p. 25). The pupa varies in length from 

 5 — y mm. (^ to ^ inch). " Small examples are found when the 

 temperature has been low or excessively hot and somewhat dry. 

 Large examples invariably occur in fermented materials, more 

 especially so in stable manure" (Newstead, p. 15). Lack of 

 moisture and consequently of available semi-liquid food seems 

 to be the principal cause of dwarfing and retarded growth. 



" In stable-middens the pupa; occur chiefly at the sides or at 

 the top of the wall or framework of the receptacle, where the 

 temperature is lowest. In such situations they were often found 

 packed together in large masses numbering many hundreds. 

 The flies emerge from the pupse, under the most favourable 

 conditions, in five to seven days. In ash-pits they occur in the 

 positions already indicated, and if similar conditions as to 

 heat prevail, the period is approximately the same; but in all 

 cases when heat is not produced by fermentation, the pupal stage 

 may last from 14 to 28 days, or even considerably more" 

 (Newstead, p. 15). 



The fly escapes from the puparium by pushing off the anterior 

 end of the pupal case in its "dorsal and ventral portions by 

 means of the inflated frontal sac, which may be seen extruded 

 in front of the head above the bases of the antcnnci;. The 

 splitting of the anterior end of the pupal case is quite regular, a 

 circular split is formed in a line below the remains of the anterior 



