HABITS OF TWO PARASITES OF BLOW-FLIES- 



203 



segments — the integument is covered with fine seta? and scattei-ed 

 sensory hairs (text-fig. 5). The mouth-parts of this stage are 

 well defined (text-fig. 6). The posterior appendage has almost 

 disappeared; easily visible just under the integument and scattered 

 about in the abdominal region are large white particles. The 

 spiracles, which are of a very simple structure, number nine pairs, 

 and appear on the second thoracic and first eight abdominal seg- 

 ments. There appears, on either side, a small main trachea with 

 segmental branches. 



Text-fig. 5. — SetcT and sensory liairs on portion of integument of full-grown larva 



of A. manducator. Greatly magnified. Original. 

 Text-fig. 6. — Head of full-grown larva, partly reconstructed, camei'a-lucida drawing. 



X 25. Original. 



During all the larval stages the mid-intestine is closed caudally, 

 and it is not until the emergence of the adult insect that the 

 residuar}^ and undigested food-matter is voided. 



The last instar larva has, on several occasions, been observed 

 feeding upon the lirpiid remnants of its host, having at some stage 

 pushed the trachefe of the host to the sides of the punarium ; 

 the latter being lined with the fly-nymph's pupal skin. It 

 seems only reasonable to assume that chitin, represented by the 

 integument of the fiy pupa, and the main tracheal trunks of 

 the blow-fly larva which remain constant in histolysis do not 

 form part of the larval diet. This postulation, if correct, would 

 exempt the Braconid larva from the necessity of eating its own 

 cast larval skins. 



Before the pro-pupal stage, the final instar larva — which by 

 this time completely occupies tlie puparium of its host — spins a 

 silken cocoon, which either adheres (a) to the thick chitinized 

 walls of the puparium, or {h) to the stretched integument of the 

 fly pupa, and which generally is caused to adhere to the walls of 

 the puparium. In {a) the absence of the fly-pupal skin w^ould 

 be accounted for by the first instar larva, having started its 

 attack before the host larva had settled down to pupate or 

 before histogenesis had started, and (6) after histogenesis had 

 started. So that the texture of this cocoon or lining to the 

 puparium is not always the same, the external portion of it — that 



Text -iigure 5. 



Text-figure 6. 



