276 T. H. Morgan 
Such considerations show at least that there are questions 
connected with sex determination that may be as impor- 
tant as the visible differences relating to the quantitative factor 
alone. At present however our evidence is largely confined 
to the recognizable quantitative changes in the chromosomes. 
A problem of exceptional interest arises in connection with 
the odgenesis of the parthenogenetic eggs that produce par- 
thenogenetic individuals (the stem-mother’s odgenesis for 
example) and of the parthenogenetic eggs that produce the 
male and sexual female individuals. Is there a synapsis of 
the chromosomes? Even though the full number of chromo- 
somes is retained, this fact does not preclude the possibility of 
synapsis. I have studied this problem with some care but the 
decision is so fraught with difficulties that [ have decided for the 
present to withhold any attempt to answer the question until I 
can give the matter fuller consideration. 
THE LIFE-CYCLE ‘OF PHYLLOXERA PALLAX 
The doubts that have arisen in regard to the identification of 
this species (see Pergande) are due to an incomplete knowledge of 
its life-cycle. Only a series of consecutive observations made at 
short intervals could reveal the relations of the successive genera- 
tions. During two years [ have made such observations and at 
the critical periods have preserved quantities of material every 
three or four days. ‘The facts discovered in the course of these 
observations show how difficult it would be to unravel the life- 
cycle without a very complete series of stages; for, the inhabitants 
of galls first formed may pass through certain phases before the 
inhabitants of later formed galls reach those stages. ‘There is thus 
an overlapping of stages. Second, the number of individuals of a 
phase in the cycle is closely connected with the size of the gall, 
which in turn is generally dependent on the time at which the gall 
is produced. ‘Third, the production of winged and wingless forms 
by the stem-mother is not the same for all galls. 
The following data give the results of observations made during 
the spring of 1908 on material collected on the Palisades north of 
Fort Lee, New Jersey. 
