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 chitinized dorsal 

 wall is well shown in Prof. Comstock's illustration (Fig. 508, 

 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, g.). 

 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 imaginal tissues, 

 which are as yet imperfectly under- 

 stood. More than thirty years ago 

 Weissman published his account of 

 the post embryonal development of Musca (CalUphora) vomi- 

 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 imaginal 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 CalUphora, and, in addition, more or less com- 

 pletely the development of a few other insects of complete 

 metamorphosis, including a butterfly, a beetle, an Encyrtus, 

 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 imaginal organs de- 

 velop from small scattered groups of primitive cells, which are 

 not derived from the cells of the larval organs, but are distinct 

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



Fig. 2 Blepharocera capilata 

 Loew ; pupa, ciorHal aHpect; 

 g., tracheal gills. 



