640 MR. G. S. COTl'ERELL ON THE LiFE-HISTORY 



described previously, except for the structure of the lateral 

 pharyngeal plates (text-fig. 8, a). These are similar in structure, 

 but are more strongly chitinised and longer in proportion to their 

 breadth. They are united dorsally by a chitinised band, and ven- 

 trally by a thinly-chitinised membrane forming the floor of the 

 pharynx (text-fig. 8, I). The median piece is replaced by a pair 

 of chitinised rods, the intermediary sclerites (text-fig. 8, h), which 

 are united transversely by a bar of chitin. Dorsal to each inter- 

 mediary sclerite and lying close up to each there is a slender 

 chitinised rod. 



The buccal sclerites are elongate and spoon-shaped (text- 

 fig. 8, cl & text-fig. 9). The exterior lateral edge of each bears four 

 teeth. Yentrally, and at the base of the hooks, there are a pair of 

 short chitinised rods (text-fig. 8, on) which support the oral 

 opening. 



The buccal sclerites of the third instar appear dorsally to 

 those of the second instar two days before ecdysis, becoming fully 

 chitinised and functional one day before ecdysis. The remainder 

 of the mouth-parts do not become fully chitinised until a few 

 hours before ecdysis. A complete second set of mouth-parts was 

 never definitely observed at this moult, but as all the mouth-parts 

 of the first instar are thrown ofi", the same may be taken for 

 granted to occur here. The new anterior and posterior spiracles 

 can also be seen underlying those of the present instar. 



The second ecdysis takes place on the third and fourth day of 

 larval life, this period lasting from 36 hours to 3 days. 



The Larva. — Third Instar. 



In the third and final larval instar the larva increases greatly 

 in size, measuring, when full-grown and f idly-extended, from one 

 to one and a half centimetres in length. The general external 

 shape is similar to that described in the preceding instars. 



The anal plate (text-fig. 11) is surrounded by twelve tubercles. 

 The two largest are situated further forward than the rest on the 

 ventral surface of the last segment immediately behind the aniis. 

 The remainder are situated on the border of the anal plate, eight 

 Ia.terally (four on each side) a.nd two dorsally. In addition, there 

 are three situated on the anal plate itself below the spiracles. 



Spines (text-fig. 12) occur on each segment fi-om the fifth seg- 

 ment posteriorly, concentrated on the anterior border. The last 

 few segments are uniformly covered. A belt of spines also occxirs 

 round the middle of the fourth segment. The anterior borders 

 of the four anterior segments bear a number of small projecting 

 plates (text-fig. 13) arranged in a number of concentric rings round 

 the segment. Each plate lies against the side of the body, but 

 is hinged anteriorly and can be pushed away from the body. 

 These help to give the first segments a grip when pushed into 

 the dung, but they can also be pulled in against the side of the 

 body if the larva wishes to withdraw its anterior segments. They 



