The origin and development of the wings of Coleoptera. 541 



the future imaginai organs i. e. wings, legs, antennae etc. The haemo- 

 lymph enters the wing through spaces between the two basement 

 membranes where they have not fused. These spaces, or sinuses, are 

 the first trace of the future veins of the wing (PI. 16, Fig. 22 v.m; 

 Figs. 23, 24 and 25 v. cos, v.s-cos., v.rm, v.m, vxu, v.a). 



The hypoderrais of the wing shows the first indications of change 

 at about the time the larva ceases feeding, when the nuclei and cyto- 

 plasm of the cells are seen to be moving towards the outer surface 

 of the wing. The cell is still attached to the basement membrane 

 by a thinner portion which later becomes a delicate structureless fibre 

 [see also Mayer, 1896] (PI. 17, Fig. 35 fhr; PI. 16, Figs. 22, 23 and 

 24). This rearrangement of the cell contents results in the formation 

 of spaces between the proximal ends of the hypodermal cells, which 

 become more or less filled with tracheoles and leucocytes, and when 

 there are ruptures in the basement membrane haemolymph and blood 

 corpuscles are also found there (PI. 17, Fig. 34). Gradually the nucleus 

 and cytoplasm move towards the surface and eventually the nuclei 

 and the cell contents become arranged in a single layer at the sur- 

 face of the wing (PI. 16, Fig, 25). This last state is attained just 

 before pupation when the wing is fully expanded and ready to be- 

 come rearranged in position to form the pupal wings. The result of 

 the migration of the cell contents is a great increase in the surface 

 area of the wings, for each cell now has its distal end many times 

 larger in area than it was at the beginning of the prepupal period, 

 and to this increase in the area of the distal ends of the cells the 

 wing owes its growth. 



A delicate layer of chitin is now secreted by the hypodermis 

 which goes to form part of the pupal cuticula ; and soon afterwards the 

 final transformation to the pupal stage occurs. During the early part 

 of the pupal stage the hypodermis proper does not show any activity 

 in growth, but towards the latter part of this stage the cells enlarge 

 slightly and some few divide so that the wing surface becomes much 

 folded, a condition frequently noted in accounts of Lepidopterous 

 wing development. This is the normal method of hypodermal growth. 

 At the final transformation these folds are flattened out and the wing 

 expands, perhaps to five hundred times its area in the pupal stage 

 (Mayer 1896). In the Coleoptera there is no such great increase 

 in the size of the wings of the imago over those ofj the pupa as 

 occurs in the Lepidoptera. Thus in L. decemlineata the ratio be- 

 tween the area of the elytra of the imago and pupa is 4:1, of the 



