THE INTERNAL STRUCTURE OF THE LEPIDOPTEROUS PUPA. 75 



cells is removed and replaced by a firmer epithelium like that covering 

 the other regions. It is this renewed hypodermis which conceals the 

 wing within, serves to separate it from the cavity of the body, and 

 gives the illusion of a complete change in its situation. 



The chitinous outer cuticula (eta.') of the pupa encloses each wing 

 in a separate sheath (PI. i., fig. 3), exhibits a stratified condition, and 

 is deeply pigmented near its outer surface (PI. i., fig. 4). A delicate 

 structureless membrane, known as the inner cuticula (eta", PI. i., fig. 

 4), lies between the outer cuticula (eta.') and the hypodermis (h'drm.). 

 At this stage each wing consists of a hollow bag, the wall of which is 

 composed of a single layer of hypodermal cells (h'drm., figs. 3 and 4) 

 which contain large oval nuclei, the latter exhibiting chromatin 

 granules arranged near the periphery. One now finds a delicate 

 membrane (mbr. pr., PI. i., fig. 4) lining the whole interior of the 

 wing-bags. This is the " grundmembran " of Semper (1857), who 

 showed that it was produced by mesenchymatous cells, which applied 

 themselves to the deep surface of the hypodermis, and sent out lateral 

 processes, serving both to connect the cells with one another and to 

 give them a stellate form. These stellate cells secrete an intercellular 

 substance, filling up the interstices of the network formed by them, 

 and this substance, together with the metamorphosed cells that pro- 

 duce it, finally become the thin structureless membrane to which 

 Semper gave the name " grundmembran." This membrane is widely 

 separated from the hypodermis as a whole, and the space between them 

 contains lymph corpuscles in large numbers (Mayer) . It appears to be 

 probable that there are communications between the sub-hypodermal 

 spaces and the chief lumen of the Aving. At rather regular intervals 

 the " grundmembran " of one wall becomes continuous with that of 

 the other by means of hollow tubes (ib., PI. i., figs. 3 and 4), formed 

 by the folding of the membrane itself. The cavities of these tubes are 

 direct continuations of the sub-hypodermal spaces of the upper and 

 lower walls of the sac. Leucocytes are frequently found within the tubes. 

 A slender thread-like prolongation of the hypodermic cells (pre, PI. i., 

 figs. 3, 4, 5) extends inward from each cell of the hypodermis to the 

 " grundmembran " ; each cell gives rise to only one, and occasionally 

 a cell is seen without any, process. The wings at this stage are still 

 little more than simple out-pocketings of the general hypodermis of 

 the chrysalis. In fact, in the larva itself the general hypodermis of 

 the body is lined on the inner side by a thin membrane, coincident in 

 relative position with the " grundmembran " of the wings, and where 

 this membrane is stretched, as in PI. i., fig. 9, the hypodermal cells 

 send out processes which are connected with the membrane. This 

 reminds us of the condition of the processes (pre, PI. i., figs. 3 and 4) 

 in the pupa. 



The wings are filled with luemolymph (blood), and this fluid con- 

 tains blood corpuscles of different shapes (leu'ey., leu'ey.' leu'ey.", PI. i., 

 figs. 3 and 4), some of which are vacuolated (leu'ey.', PI. i., figs. 4 

 and 5) and appear to be corpuscles in the course of degeneration. Mayer 

 supposes that these are the fat cells of Semper. 



About three weeks before the insect will emerge (a less period, of 

 course, in those species in which the pupal period is very short), 

 "certain of the hypodermic cells (cl. frm., PI. i.,fig. 5), which occur 

 at regular intervals, begin to be modified. They commence to increase 



