644 



MR. a. S. COTTERELL ON TUE LIFE-HISTORY 



intermediary sclerites were thrown off, but it seemed impossible 

 that the larva could be capable of throwing off the large lateral 

 pharyngeal plates. No conclusive proof was obtained of the 

 complete throwing-off of the second instar mouth-parts at the 

 second moult, but this may be taken for granted as occurring as 

 well as at the first moult. 



The total larval life takes from 9 to 12 days. The minimum 

 time observed was 8 days and the maximum 14 days. Eleven 

 days is the usual length of time under laboratory conditions. 



The total larval life and the ultimate size of the larva, and 

 therefore the puparium, are controlled to a very large extent by 

 the temperature and condition of the breeding medium. Lack of 

 moisture is a very important factor. This explains the variety 

 in size of the adults. 



The Puparium. 



At pupation the two anterior segments of the larva are with- 

 drawn, bringing the anterior spiracles in a forward position. In 

 this position the larval skin slowly changes to the brick-red 

 colour characteristic of the puparium (text-fig. 14). The colour 

 changes to black as the pupal period advances. It is more or 

 less cigar-shaped ; the anterior end is slightly flattened dorso- 

 ventrally. The anterior spiracles can be seen as two dark 

 projections at the anterior end. It raeasures from 6 mm. to over 

 a centimetre in length. The size varies according to the con- 

 ditions governing the life of the larva, mentioned earlier. 



From larvfe bred in the laboratory a large percentage pupated 

 in the hardened upper crust of the dung. This was probably due 

 to the soil being too moist in the jars, as there was no outlet 

 to allow the excess moisture to get away. Under ordinary 

 conditions the soil is preferred, as in field observations very few 

 puparia were observed in dung. 



The pupal period takes from 10 to 17 days. The minimum 

 time observed was 6 days and the maximum 18 days. 



The following data give the comparative larval and pupal 

 periods for a number of batches bred : — 



