357 



formation. Sometimes the narrow lumen of the leg contains 

 these cells in large numbers; occasionally one may be seen 

 among the loose epithelial cells of the leg. In the early pupa 

 the leucocytes appear quite healthy, although heavily gorged 

 with larval tissues; but gradually they disintegrate, or 

 recovering, wander away, and are no longer seen here in a 

 two-day pupa. The disintegration will be described more fully 

 in connection with the blood. 



A single tracheal vessel enters into each leg soon after 

 its formation (fig. 65), 



The formation of the muscles of the leg and of the great 

 tendon will be more conveniently considered in connection 

 with the muscular system. 



The development of the last tarsal segment is worthy of 

 special attention. Already in the eight-hour pupa the 

 segment is slightly larger and wider than those which precede 

 it. As development proceeds this process continues, producing 

 a claw-bearing segment considerably wider than the others. 

 The ectodermal cells, moreover, do not remain as a single 

 layer but proliferate, producing two masses of padding 

 tissue, very similar to that which is formed in the bulging 

 segment of the antennae. These masses are clearly visible in 

 the pupa of thirty-six hours. The epidermal cells on either 

 side of them, and aJso at a place on the ventral side slightly 

 proximal to them, grow out in the form of large claws. 

 Chitinisation then takes place. The cells of the three claws 

 almost totally disappear; the pads, however, secrete only a 

 very thin membrane of chitin, which arranges itself in two 

 pairs of long pads, structures which are probably to be con- 

 sidered as adhesive organs. They are shown clearly in fi.g. 46, 

 which is from a pupa of four and a half days. The distal part 

 of these pads is totally devoid of cells, the padding cells being 

 confined entirely to the main portion of the segment. The 

 proximal part of the padding tissue is syncitial in nature and 

 on it is inserted what appears to be a tendon (fig. 46). It is 

 quite possible that a pull of this tendon would draw back the 

 padding tissue and apparently also the thin chitin which it 

 has secreted. If the joint had been placed previously on some 

 solid object it is conceivable that a partial vacuum might be 

 created between the four adhesive pads and the object, thus 

 enabling the wasp to cling to a smooth surface. The capacity 

 of chalcid wasps for clinging to window glasses is, of course, 

 well known to all who have collected them. 



The Wings. — The general features of the development of 

 the wings have been described above; it remains to describe 

 now the histological changes which they undergo. 



