MORPHOLOGY OF THE ALEYEODIDjE. 15 
appearance, for here the ring of spinnerets is not extended into rod- 
shaped structures, but is seen only at the base. The outer cup is very 
shallow and the central chitinous process is split into a number of 
sections. It would appear that in Paralcyrodes the spinnerets and 
outer cup have become shortened at the same time with the media 
and radius^ The compound pores of the forms belonging to the 
subgenus Met aleurodicus are of an intermediate nature. The spin- 
nerets are reduced in minima and cardlni in a manner comparable to 
those of Paralcyrodes, but the central process is entire. In dltissimns 
besides the reduction of the spinnerets, the central process is split into 
three divisions. In these forms, however, the lingula is short and 
generally included, unlike the typical forms of Aleurodicus or 
Paraleyrodes. Unfortunately the adult of altissimus has never been 
secured as, from the pupa, it appears to be a very interesting form; 
but whether it is nearer Paraleyrodes or Aleurodicus can be decided 
only by an examination of all the stages. 
RESPIRATORY SYSTEM. 
The respiratory system in Aleyrodicla? seems to be more fully devel- 
oped in the larval stages than in the adults. In some forms, as in 
those belonging to the citri group, there are in the immature stages 
special breathing folds developed which are often indicated on the 
dorsal surface by sculpturing and the outer extremity of each is 
guarded by stellate or other serrations on the margin of the case. 
The folds are three in number, there being a latero-thoracic pair and 
a caudal fold, this latter extending from the vasiform orifice caudad 
to the margin and forming a Y-shaped structure which extends to the 
posterior thoracic pair of spiracles. In some species, even when the 
thoracic folds are not noticeable, the caudal fold will be long and 
deep. The courses of the various tracheae have been worked out by 
Woodworth for Aleyrodes citri* and the observations of more recent 
writers on the subject, as well as those made by ourselves, only sub- 
stantiate his findings. 
In the adult the system follows the same plan as in the larva. 
There are the same number (four pairs) of spiracles present, one pair 
of which is abdominal and situated near the vasiform orifice. The 
trunks and girdle are, however, much more reduced in the mature 
insect. 
METAMORPHOSIS. 
The metamorphosis in this family has always been an interesting 
and problematical subject of study. During the later larval stages 
the antennae, mouthparts, and legs become, to a certain extent^ atro- 
phied. In the pupal stage, however, they appear to be, in some cases 
at least, functional. In Dialeurodicus cockerellii, for example, there 
