STRUCTURES OF PUPA 101 



siderably greater than in the adult. . . . That I may not have to refer to these 

 parts again, I will at once say that the chief changes which occur in them during 

 pupal life are : (1) The development of a cuticle within the pupal cuticle, and 

 this, in the case of the labium (fused second maxillae), is covered with scales 

 closely resembling those found in Lepidoptera ; (2) a considerable shrinking; 

 (3) in the male only, atrophy of the mandibles, which in a young pupa are as 

 large as in the female, but in the adult are not recognisable. 



" The antenncE, which were folded and telescoped at their bases in the larva, 

 are in the pupa laid upon the sides of the thorax. . . . Their hinder (distal) 

 extremities are hidden by the wings. The swollen basal joint of the antenna of 

 the imago is hardly recognisable on the surface, although it is already a con- 

 spicuous object in sections of the youngest pupae, and even in the larval state. I 

 shall describe it with the other sense organs. The shaft of the antenna is seg- 

 mented, but the external segmentation loses its correspondence with the seg- 

 mentation of the developing antenna within it early in pupal life. 



" The thorax is large and rounded, but somewhat compressed from side to 

 side. Mid-dorsally the cuticle of the prothorax * is marked by fine transverse 

 corrugations, and this is the part which ruptures to allow the imago to escape. 

 A pair of branched setae arise from the dorsal region of the hinder part of the 

 thorax. 



" The respiratory siphons are nearly cylindrical, narrowed at their bases and 

 curved forAvards to be attached by flexible membranes to slight prominences on 

 the sides of the prothorax.* Above they are obliquely truncate and open, and 

 the margin is slightly notched on the inner side. The outer surface is marked 

 so as to resemble imbricated scales, each with a minute spine at its apex. The 

 cavity of the siphon communicates directly with that of a tracheal trunk at its 

 base. Palmen says that after a ' close investigation ' he has found that there is 

 no opening. The tone of assurance in which he contradicts all previous observers 

 led me to put the question to the test. I removed the side wall of the thorax, 

 with some of the underlying muscles and tracheae, from a specimen pre- 

 served in alcohol. I drew out the alcohol from the cavity of the siphon by means 

 of blotting-paper, and then touched the tip with a minute drop of glycerin. I 

 watched the effect under the microscope, and saw the glycerin force its way into 

 the siphon, driving the air before it into the trachea?. Palmen, morover, says 

 the organs are gills ! Each is a thick chitinous tube, the cavity guarded by nu- 

 merous hooked spines, the walls consisting of hardly anything but the chitinous 

 cuticle, the epidermis (' hypodermis ') between its two layers being barely recog- 

 nisable on account of its thinness. The ' tracheal gills ' on which Palmen lays 

 much stress have absolutely no existence. 



" The tvings of the pupa, that is the organs within which the Avings of the 

 imago are developing, are a pair of oblong plates about 2 1/3 mm. in length. 

 They are closely applied to the sides of the hinder part of the thorax, and 

 directed downwards and backwards. They are immoveable. 



" The halteres are a pair of elongated triangular plates lying along the dorsal 

 and hinder border of the wings. 



" All these three pairs of dorsal appendages arise within the larva in the same 

 way, and their bases or points of attachment all lie in the same horizontal plane. 

 Each is at first (in the larva) a fold of the epidermis ; each acquires a cuticular 

 covering (like all other parts of the body), and the first pair become rolled up 

 to form tubes, the respiratory siphons, while the other two remain flat plates. 



" The three pairs of ventral appendages of the thorax, or legs, are long cylin- 

 drical bodies folded upon themselves, and lying beneath the thorax and between 



* This is in reality the mesothorax. The prothorax is represented by a very smaU field 

 anteriorly, just above the base of the antennte. II. D. & K. 



