MORPHOLOGY OF THE ALEYRODIDiE. 5 
The duration of the egg stage is about 12 days for the commoner 
forms. Temperature, however, seems to have a considerable in- 
fluence upon the length of the stage, for in uniformly warm weather 
a much shorter time is necessary and under unfavorable circumstances 
the time may be greatly extended. The larva emerges from the egg 
by means of a longitudinal fissure in the anterior part of the egg and 
the time required for escaping from the shell varies considerably. 
In connection with her studies of Aleyrodidae in California, Miss 
Bemis observed the hatching of numerous eggs and says : 8 
In the eggs under observation, there elapsed from forty-two minutes to three 
hours and eight minutes from the time that the shell began to open until the 
larva was free. The egg that took the greater time was upon dry material 
and was dark brown in color, the shell when empty keeping its upright posi- 
tion and shape, so that the slow hatching was probably due to the toughness of 
the chorion. 
In our experience the drying of the material upon which the eggs 
are placed greatly retards or even prevents hatching. 
THE HEAD OF THE ADULT. 
The head is somewhat triangular in shape and is carried in such 
a way that its anterior surface is slanting ventro-caudad. The 
compound eyes are of the agglomerate type. They are usually con- 
stricted in the middle (reniforrn), or in some species are entirely 
divided by a tongue-shaped portion of the integument. It some= 
times happens also that the facets of these two sections are different 
in size. The ocelli are two in number and situated close to the an- 
terior margin of the compound eyes. The position of these ocelli 
relative to the compound eyes varies in the different species. 
The antenna? are placed below the eyes in shallow antennal sockets. 
They bear a striking resemblance to those of the Aphididse. As a 
rule, they are composed of seven segments, of which the third is the 
longest. The first and second are always short and thick, while the 
others are elongate, subcylindrical, and covered with numerous imbri- 
cations. Circular fringed sensoria occur usually on segments III, V, 
and VII (see Alearodieus giganteus, PL XXIV, fig. 10), and spike 
sensoria are sometimes also found. Fine hairs are scattered here and 
there or are found encircling the segments, and segment VII always 
terminates in a bristle-like armature. There is great variation in the 
length of the segments among different species in the genus Aleyrodes 
as at present understood. As a rule, segment VII is short, often the 
shortest of all. In species like graminicola, however, it is as long as 
all the other segments together and in longicornis very much longer. 
This variation may prove to be of importance in dividing the genus 
when the forms have been carefully studied. In Paraleyrodes seg- 
ments III to VII have become united so as to form two. 
