HABITS OF T\YO PARASITES OF BLOW-FLIES. 203 



segments — the integument is covered with fine setpe and scattered 

 sensory hairs (text-fig. 5). The moutli-parts of this sttige are 

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

 disappeared ; ea.sily visible just under tlie integument and scattered 

 about in the abdominal region are large white particles. The 

 spiracles, which ai'e 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 -figure 5. Text-figure 6. 



- - ^ ^ >^ 



^ *< ^ \^ 



Text-fig. 5. — SetiE and sensory hairs on portion of integument of full-grown larva 



of A. manducator. Greatly magnified. Original. 

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



X 25. Original. 



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

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

 lesiduar}'- and undigested food-matter is voided. 



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

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

 pushed the tracheJB of the host to the sides of the puparium; 

 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 fly 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 

 ca,st larval skins. 



Befoi'e the pro-pupal stage, the final instar larva — which by 

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

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

 walls of the puparium, or (h) to tlie stretched integument of the 

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

 the puparium. In («) the absence of the fly-pupal skin would 

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

 attack liefore the host larva had settled down to jjupate or 

 before histogenesis had stai-ted, and (&) 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 



