340 



wing occupies, in the twenty-four hour pupa, an area about 

 three-quarters the size of the wing of the newly forme-d pupa 

 (fig. 44). Already in the pupa a few hours old, the upper 

 and lower pairs of veins of the fore wing are seen to lie 

 each within a broad clear space, extending from the base of 

 the wing to a distance about one-fifth the length of the wing 

 from the end. In the twenty-four hour pupa these clear areas 

 have become much more distinct. In the hind wings, so far as 

 I could observe, only a single such clear area is formed. The 

 wings meanwhile have assumed, more nearly, their adult 

 shape, showing now a very slender proximal region, and 

 developing, at the same time, each a small basal structure 

 provided with a number of irregular prominences and depres- 

 sions (fig. 9), which articulate with, or into which fit, other 

 depressions and projections from the sides of the thorax. 



The wing now assumes a remarkable appearance; instead 

 of remaining as a smooth fleshy structure, its surface begins 

 to undergo, in the thirty-six hour pupa, a very pronounced 

 folding (fig. 37) ; at the same time hairs — the fine pubescence 

 of the adult wing — as well as bristles, and the hooks of the 

 hind wings begin to appear on the surface. The folding is 

 soon complete, and the whole structure now begins to chitinise. 



The chitin on the hooks of the hind wings becomes fairly 

 thick; elsewhere, however, the chitin remains thin, and 

 closely follows the contours of the wrinkled surface of the pupal 

 win^. 



The anterior clear space of the fore wing, and that of 

 the hind wing become brown in colour ; they form the nervures 

 of the adult wings; the bifurcated clear areas on the rear 

 half of the first wing do not change colour, and remain as 

 colourless "pseudo-nervures," so characteristic of the wings 

 of many chalcid wasps. 



On emerging from the pupa the wings of the wasp soon 

 straighten out. Not till now can we actually estimate the 

 extent to which folding of the wing epithelium has taken 

 place; for so pronounced has been the folding within the 

 limited space afforded by the pupal cuticle covering the wings, 

 that these, on expanding fully, attain, in the course of a few 

 minutes, an area sixteen times that of the pupal wing. 



At the rear of the fore wing a slight turning over of the 

 wing chitin forms the only structure on which the great 

 hooks of the hind wing can possibly find a grip. 



The actual cellular processes which underlie this remark- 

 able development of the wings will be described later (see 

 page 359). 



One point seems to be worthy of special attention here. 

 The fact that the clear spaces (developing nervures) of the 



