THE WILLOW GALL-FLY. 567 



under the name of Caddomyia Salids.* On account of the 

 size of the larva and the ease with which it may be raised, 

 it is an excellent object for the observation of the transfor- 

 mation that is peculiar to it and to other species of the genus. 

 It inhabits a small woody gall, growing at the ends of the 

 slender twigs of the American basket-willow QSalix rigida), 

 and other dwarf willows. This kind of gall is of an oval 

 shape, about three quarters of an inch long, by three eighths 

 of an inch thick, and is terminated by a brittle conical beak, 

 which seems to me to consist of the unexpanded and dry 

 terminal bud of the twig. Upon being cut open in the 

 winter or spring, a longitudinal channel will be found in the 

 middle, extending from the apex of the beak nearly to the 

 base of the gall, and lined in the upper part with a delicate 

 silken web. Within this hollow is lodged a single orange- 

 colored maggot, about one fifth of an inch long. In the 

 spring this maggot takes the pupa form, the approaching 

 change being marked by an alteration of the color of the 

 anterior segments, which from orange become red, shining, 

 and swollen, as if distended with blood. Within a few hours 

 after this change of color, rudimentary legs, wings, and 

 antennae, begin, as it were, to bud. and put forth, and rapidly 

 grow to their full pupal dimensions ; and thus the transfor- 

 mation to the pupa is effected without any moulting of the 

 skin of the larva. In a few days, the pupa works its way 

 upwards, bursts through the silken film, and rests half-way 

 out of the orifice of the beaked summit of the gall, where 

 it casts off and leaves its pupa-skin, and appears in its 

 winged form. This little gnat or fly is of a deep black 

 color above, paler and downy beneath, with livid legs and 

 smoky wings. The length of its body is a little over one 

 fifth of an inch, and its wings expand rather more than three 

 tenths of an inch. 



The Cecidomyia Mobinice, of Professor Haldeman,f is a 



* American Quarterly Journal of Agriculture and Science, Vol. I. p. 263. 

 t American Journal of Agriculture and Science, Vol. VI. p. 193. 



