1900] 



ENTOMOLOGICAL NEWS. 



311 



pairs of much larger, thicker, finger like processes, which may 

 be tracheal gills of another kind. 



II. 



The Pupa. The peculiar shape of the pupa, with its flat 

 ventral aspect and strongly convex, heavily chitiuized dorsal 

 wall is well shown in Prof. Comstock's illustration (Fig. SOS, 

 Manual of Insects). The pupa has a pair of dorsal, pro- 



thoracic tracheal gills, each one of 

 these organs consisting of four small 

 elliptical, erect plates (Fig 2, </.). 

 The whole of the flat ventral aspect of 

 the pupa is applied to the rock, and 

 the pupal cuticula is thin and mem- 

 braneous. The wings and legs are 

 folded on this flat ventral aspect. 



In the interior of the pupal body 

 occur the interesting phenomena asso- 

 ciated with the histolysis of many of 

 the larval tissues and organs and the 

 histogenesis of the imagiual tissues, 

 which are as yet imperfectly under- 

 stood. More than thirty years ago 

 Weissman published his account of 



FIG. 2 Blepharocera capi/ata 

 Loew ; pupa, dorsal aspect; 

 g., tracheal gills. 



the post embryonal development of Musca (Calliphnru) 

 toria, in which he told of the great breaking down or disinte- 

 gration undergone by certain larval organs and of the devel- 

 opment of the imagiual wings and legs from small groups of 

 cells called imaginal discs, which could be found in the larva. 

 at an early age. Since then a few men have restudied the de- 

 velopment of Callijiliorti, and, in addition, more or less com- 

 pletely the development of a few other insects of complete 

 metamorphosis, including a butterfly, a beetle, an /-,W//r///.v, 

 the little brown ant, and a few others. What has been found 

 out is chiefly this, that in insects with complete metamorpho- 

 sis many of the larval organs and tissues disintegrate during 

 the pupal stage, while the corresponding imagiual organs de- 

 velop from small scattered groups of primitive cells, which ;nv 

 not derived from the cells of the larval organs, but are dist inet 

 from them ; some of them are, indeed, derived directly from 



