296 Titel s Morgan 
The last figure, Plate I, Fig. 9, is from a small leaf gall with 
a short nipple opening beneath. When open, four or five short 
bracts border the margin. The galls seem to corresp ond to P. 
depressa, but again the description is too imperfect to make identi- 
fication certain. 
‘These figures show, I hope, the value of this stage in the life cycle 
for systematic identification. Until this stage has been further 
studied in more species, and until their relation to the sexual forms 
is known, our knowledge of the genus must remain, as at present, 
most fragmentary. 
In connection with the study of the sexual (?) forms of these 
species I have also studied the chromosomes of the equatorial 
plates of the migrants in the hope that a knowledge of the chromo- 
some number might help in disentangling the systematic identifica- 
tion of the species, but also and primarily in the hope of discover- 
ing whether two types of chromosome groups exist where only one 
sexual (?) form has been discovered. ‘The first question can be 
answered decisively; the second, with less certainty. ‘The chro- 
mosome groups are sufficiently different to aid materially in identi- 
fication. Within these species I have not been able to distinguish 
two types of polar spindle plates as in P. caryzcaulis and occasion- 
ally in P. fallax, but the number of individuals found with per- 
fectly distinct groups of chromosomes has not been large (despite 
the great amount of labor expended in finding the polar spindles) 
so that I should not like to speak positively on this point. 
Polar plates of the polarspindle of theeggsof P. caryzeglobulare 
shown in Fig. XIX, G, H. ‘Twenty-two rounded chromosomes 
of very different sizes have been counted in several platgs. As I 
pointed out in 1906, it is interesting to find so large a number of 
chromosomes within the genus in which the winged individuals are 
so closely similar. Evidently the number, as such, is of no signifi- 
cance. 
In P. depressa there are six chromosomes (Fig. XIX, J, ‘f) four 
large and two small, as determined by a polar spindle of the stem- 
mother’s egg and by a late nuclear stage of the same sort of egg. 
In a species whose sexual form I have not yet obtained, P. caryz- 
foliz, the polar plates show eight chromosomes of different sizes 
