20 
to trace a connection between them and the Aleurodiform genera- 
tions. Continued observations, both in the woods and on small, 
potted birches to which the insects were transferred, removed, how- 
ever, all doubt as to the close relationship of these aberrant forms. 
This generation develops in time into the return migratory generation. 
Sixth generation; return migrants; first stage.—By the end of 
August or early in September the females of the last Aleurodiform 
generation, after having become fully mature, proceed to produce a 
supplementary generation of larvee, and continue to do so until 
exhausted. The number of larvee produced by each female varies, as 
in previous generations. As a rule, however, they appear to be more 
prolific, since I have observed in one female about thirty embryos, in 
consequence of which, in favorable years, the underside of the leaves 
of birches may become completely covered with larve of them in vari- 
ous stages of development. 
The recently deposited larvee are barely 0.2™" in length, oval, and 
of a yellowish-brown color, changing gradually to purplish-brown, 
with antennze and legs whitish. They are at first naked, but soon 
become covered with a pruinous or bluish-white secretion, giving 
them a moldy appearance. After growing forsome time, there forms 
a broad, medio-dorsal stripe of evenly shorn, dense and bristly, white 
and iridescent threads of waxy secretion. A dense fringe of similar 
glistening threads surrounds also the entire body, leaving the subdorsal 
region each side of the median line bare or only covered with a powdery 
secretion, and look now quite unlike the Aleurodiform generations. 
They are rather convex; the head is narrower than the thorax and 
arcuate in front; eyes larger than before; abdomen small or only 
about one-third the length of the entire insect. The number and 
arrangement of the tubercles surrounding the body is as in previous 
generations. In addition to tubercles, there are now two median 
groups of two or three very distinet pores or tubercles on the head 
slightly in front of the eyes, four medio-dorsal groups of three to five 
pores or tubercles on each side of the thoracic, and two groups of one 
to three pores each on the abdominal segments except the last. 
Antenne, legs, and rostrum are very much as before. The third 
antennal joint is fusiform, slightly annulated, and bears from one to 
three minute thumbs near the apex. The upper digitules of the 
tarsi are slender and distinetly capitate. The lower digitules are 
wanting. 
Sixth generation; second stage (Fig. 9).—Length of body, 0.4 to 
0.6". In coloration and general appearance they are similar to 
larvee in the first stage, though they are considerably larger and 
stouter in proportion, with the sides of the pro- and mesothorax con- 
siderably swollen. They are now densely covered with a white and 
glistening, straight and evenly shorn, hair-like secretion, issuing from 
large, more or less confluent medio-dorsal and lateral compound 
glands or tubereles, which, on the abdomen, form broad, transverse 
