327 



quite incapable of defaecating. The first two segments bear 

 ventrally a large, powerful, chitinous "rack," the tentorium, 

 which acts as a support for many of the muscles in the 

 anterior region of the animal. The tentorium consists of 

 three chitinous bars — really thickenings of the larval cuticle — 

 two lateral ones, bent outwards, and an anterior connecting 

 bar; while, behind, the structure is supported by a very 

 powerful chitinous bar which is formed in the embryo as a 

 secretion from a pair of epithelial ingrowths from the walls 

 of the second segment. 



The anterior three bars are shed at each moult, and re- 

 formed on the new cuticle; they do not reappear in the pupa. 



Tlie mouth is a rather small, transversely elongated, oval 

 slit, and is armed on either side by a pair of minute, sharply- 

 pointed triangular mandibles, capable of quite active move- 

 ment. The head is provided in front with a pair of very 

 minute processes, evidently having some sensory function; 

 their nature will be referred to more fully below. 



No other appendages are present. 



Four pairs of spiracles occur; one on the third segment, 

 the next on the fifth, the third on the sixth, and the last on 

 the seventh. 



The larva feeds rapidly and shows a great increase in 

 bulk, an appearance which is accentuated by the inability of 

 the larva to void the intestinal contents. Feeding takes place 

 by the application of the mouth to a hole torn in the integu- 

 ment of the fly nymph by the sharp larval jaws, the food being 

 sucked up into the buccal cavity of the larva. The larva 

 itself does not appear to move from it« orginal place of 

 feeding. 



After about thirty hours the larva moults; the second 

 instar differs from the first only in its greater size, and in 

 the presence now of a set of nine spiracles. 



The larva undergoes several other moults, but it is very 

 difiicult to determine their number, as the various instars 

 cannot be recognized by any structural differences. Maud 

 Haviland (1920 and 1921) found four instars in two other 

 chalcid wasps, species in which differences in the various 

 larvae were very obvious. 



After feeding for about three days the larva enters upon 

 the ''resting stage^\- food is no longer taken up, and a number 

 of remarkable processes begin within the body of the larva. 



Eventually after about a day the larva defaecaW, the 

 contents of "the intestine being voided as minute rounded 

 greyish or black pellets; as a result the larva changes from 

 a dirty grey to a pure white colour. 



During the next twenty hours — the post-defaecation 



