THE WILLOW GALL-FLY. 
567 
under the name of Ceeidomyia Salicis* 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 orano-e- 
o o o 
colored macrsot, about one fifth of an inch Ions. 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 Avay 
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 Ceeidomyia Rohinice^ of Professor Haldeman,f is a 
* American Quarterly Journal of Agriculture and Science, Vol. 1. p. 263. 
t American Journal of Agriculture and Science, Vol. VI. p. 193. 
