359 



disappeared, except a number on the outer edge of the wing; 

 these persist throughout the life of the wasp in a half disin- 

 tegrated state; their presence can easily be revealed by stain- 

 ing the wing of a properly preserved insect (fig. 38). The 

 outlines of the cell of the pupal wing are also clearly visible 

 around the border of that of the imago; they are beautifully 

 seen in the great fastening hooks of the hind wings, as long 

 projections into the wing, and evidently give special strength 

 to these structures (fig. 38). 



By this extensive folding of the free surface of the cells, 

 the great extensions in the size of the wing take place; so 

 pronounced indeed is this, that, as already mentioned, th^ 

 wing directly after the imaginal moult, expands to an area 

 sixteen times that of the pupal wing. 



The obliteration of the cavity of the wing, as described 

 above, however, is not complete ; on the contrary, the first wing 

 preserves an anterior (marginal) and a median longitudinal 

 ''sinus," in the form of two great channels passing down the 

 wing (fig. 44). The anterior one i?. bifurcate distally. The 

 hind wing presents only one such channel. These channels 

 are the ''clear spaces" described above as visible in a surface 

 view of the wing, and into these channels pass the tracheoles 

 of the wing ; leucijcytes are also seen here during early pupal 

 life; they disintegrate later (just as they do in the other 

 a ppendages) , but some may be seen even into the fourth day 

 of the pupa. 



If a newly found pupal wing be examined in sections a 

 remarkable thing is seen. The mesodermal cells a little beyond 

 the base of the wing begin to proliferate, and then extend as 

 a long column of cells right down the greati fissures in the wings 

 (fig. 45). No such structure, however, ever extends (in Nasonia) 

 into the median channel of the fore wing, though this channel 

 does lodge tracheoles and leucocytes; it remains indeed 

 merely as a "pseudo-nervure," while the marginal structures 

 in both wings develop into true nervures. The cells of these 

 columns are elongated and "brick-like'' in shape; the growth 

 of the column is very ro.pid and is complete several hours 

 after pupation. Late in pupal life the internal "lining" of 

 the great channels begins to chitmise slightly; the chitin is 

 pale yellow in colour, and to this the characteristic coloura- 

 tion of the nervure is due. 



To what the unfolding of the wrinkled wing at the 

 emergence of the wasp is due is difficult to say. While 

 not attempting to discuss its cause in all insects, I may say 

 that the usually accepted view, viz., that it is produced by 

 the passage of air into the tracheae^ of the wing, must be dis- 

 carded in the case of Nasonia. Here the tracheoles are very 



