5) 
dry galls on the leaves of the witch-hazel. Here I began again my 
search for the evading generations of this species, and in examining 
the leaves of birches rediscovered on many of them the same peculiar 
Aphid which had previously been found at Tacoma. It was in 
various stages of development, including the winged migrants, which 
proved, after a thorough examination and comparison with the spring 
migrants of the witch-hazel, to be identical with Hormaphis hama- 
melidis. To be sure of no mistake an examination was made of the 
leaves of witch-hazels near the birches with the result that the under- 
side of numerous leaves was found to be almost completely covered 
with larve of various stages, and among them numerous specimens 
of the migrants from birch, actively engaged depositing their progeny, 
which later on proved to be the sexual generation. This settled the 
previously obscure question as to the secondary host of the interme- 
diate generations, and.enabled me to continue and to complete my 
protracted observations of the life history of this remarkable little 
species and the strange transformations it undergoes on the birches, 
- which will be recorded in the following pages. 
HORMAPHIS HAMAMELIDIS Fitch. 
Gall (Fig. 1).—The more or less rapid development of the galls pro- 
duced by this species on the leaves of the witch-hazel depends entirely 
on the advancement or retardation of the season. In the latitude of 
Washington, D. C., they usually start about the middle of April, 
attaining their full growth and development toward the end of May. 
To be in time and ready for the duty assigned to them by nature, the 
young stem mothers hatch about a week or more in advance of the 
appearance of the young leaves, when they frequently congregate in 
considerable numbers on the still closed buds, patiently awaiting 
their bursting. During this critical period many of them perish, 
either for want of food or from the inclemeney of the weather. The 
survivors settle at once on the underside of the tender and unfolding 
leaves, generally along the midrib or the lateral veins, and insert at 
once their sucking bristles into the tender substance of the young 
leaf. The presence of the young gall-maker soon becomes apparent on 
the upper side of the leaf by a pale yellowish-green discoloration, and 
within a few days the first symptoms of the growth of the new gall 
are Observable in a small, blister-like swelling on the upper side and 
a corresponding depression beneath. From now on the development 
of the new gall is quite rapid, in order to keep pace with the growth 
of the leaf, so that at the beginning of May they have become quite 
convex or slightly conical above with the underside almost closed and 
protected by numbers of rather stiff, white,and radiating hairs to 
prevent the entrance of enemies. The color of these young galls, 
above and below, is of a greenish yellow, with the most elevated 
portion of a more or less pronounced vinous shade and surrounded 
