660 TEXT-BOOK OF ENTOMOLOGY 



were about to pupate, he produced an artificial metamorphosis by 

 removing the cuticula in small bits. Exposing the appendages in 

 this way, they preserved the position which they are seen to take 

 during growth. Each wing appeared within the limits of the seg- 

 ment from which it grew out (Fig. 610), not extending beyond, 

 as it does in the normal pupa, so that Reaumur was wrong in saying 

 that " the wings are here gathered on each side into a kind of band, 

 which is large enough to lie in the cavity which is between the 1st 

 and 2d segment." (8 e Mem., p. 359.) 



All these parts are coated with a viscous fluid secreted by special 

 glands, which hardens after pupation upon exposure to the air. So 

 long as the parts are soft, they can easily be displaced. Gonin drew 

 one of the antenna like a collar around the head, and one half of 

 the tongue upon the outer side of the wing. 



" When pupation is normal, the integument splits open on the back 

 of the thorax, and the pupa draws itself from before backwards. 

 Owing to the feeble adherence which the chitinous secretion gives it, 

 it draws along with it the underlying organs. The legs, antennae, 

 the two halves of the tongue (maxillae) retained by their end, each 

 in a small chitinous case, can only disengage themselves from it 

 when in elongating they have acquired a sufficient tension. The 

 curves straighten out and the folds unbend. The chitinous mask of 

 the head in withdrawing from the larval skin follows the ventral 

 line ; the tongue and labial palpi free themselves from its median 

 part; the antennas disengage themselves from the two lateral scales. 

 Between these different appendages a space is left on the surface of 

 the head for the eyes, and on the thorax for the legs. These are 

 not completely extended on account of the lack of freedom of the 

 femoro-tibial articulation; the femur preserves its direction from 

 behind forwards, and the knee in the two first pairs remains at the 

 same height. The wings overlie them and cover the under side of 

 the two basal abdominal segments ; their surfaces in becoming 

 united increase much in size." 



As the chitinous frame of each spiracle gradually detaches itself, 

 we see a tuft of tracheae passing out of the orifice. It is at this 

 moment that the provisional tracheal system is cast off, and it is 

 easy to see that the process is facilitated by the simultaneous elon- 

 gation of all the appendages. The permanent tracheae can follow 

 this elongation because they are sinuous, and need only to straighten 

 their curves. It is, however, not the same with the tracheoles, as 

 we have seen in the case of the wings (p. 133), and their extension 

 or stretching is thus explained by a very simple mechanism. 



