1. TRÄGÅRDH, METAMORPHOSIS AND BIOLOGY OF ORCHESTES. 7 



The abdomen shows the concentrating of the last seg- 

 ments which takes place in the adult. Topographically, on 

 dorsal view, the 8th abdominal segment is the terminal one, 

 but on ventral view we notice a small 9th segment which 

 is subventral, and on closer examination we notice traces 

 of the lOth and llth segments (Textfig. 1). 



The 7th abdominal segment projects in two conicals dark- 

 coloured processes which have a small black spine at the 

 top; even the 8th segment has small conical processes. 



Biology. 



The female deposits the eggs on the lower side of 

 the leaf, of ten in considerable number; the author has 

 counted up to 20 on a single leaf, but generally there are 



Fig. 1. Top of abdomen, ventral view. 

 Pupa of O. populi. X 50. 



5—10. The female bores an oval hole through the epidermis 

 of the leaf, in which the egg is placed, and from this the 

 larva works its way to close below the upper surface. (Fig. 

 20. Pl. IT). 



The larva does not form any gallery, but a rounded 

 blotch-mine. This is very conspicuous through its bright 

 yellowish-brown colour. When the blotch is small, the upper 

 cuticle of the leaf is quite flat, but låter, when it increases in 

 size, the thin cuticle rises above the surface. On the lower 

 side of the leaf, on the other hand, only a small indistinct 

 patch is discernible. 



If we open a blotch-mine, we find that the floor is for 

 the greater part almost black; this is, as already pointed 

 out by Letzner, due to its being impregnated with the ex- 



