PREDETERMINATION OF SEX 289 



THE POLAR 8P1NDLE OF THE MALE EGG OF PHYLLOXERA FALLAX 



In my earlier work I did not obtain any anaphase stages of the 

 polar spindle of the male-producing egg of this species; although 

 a number of equatorial plates were obtained and figured. For 

 certain reasons, that need not now be given, it became evident 

 that this stage in this species should give an answer to certain 

 questions and a long search for anaphase figures was begun. In 

 P. fallax the eggs are laid one after the other by each female. 

 Hence not more than a few eggs in the desired stage could pos- 

 sibly occur in a single gall, which renders the .chance of finding 

 such a stage very small indeed. Nevertheless, one excellent ana- 

 phase was found by Miss Wallace, and is drawn here in plate 1, 

 figure g. As shown in the figure, there are two lagging bodies in 

 the middle of the spindle that are conspicuous by their large 

 size. At the inner pole there appear to be ten chromosomes, 

 at the outer pole eight or nine chromosomes. 



The equatorial plate from which this figure developed must 

 have contained twelve chromosomes, since this number of chro- 

 mosomes has always been found present in such a plate. Of 

 these, eight were autosomes and have divided, so that eight 

 daughter chromosomes go out into the polar body and eight re- 

 main in the egg. The four sex chromosomes, that are pre- 

 sumably paired at this time remain to be accounted for. If the 

 two bodies seen in the middle of the spindle are two whole X 

 chromosomes, then there can be but eight in the outer plate (which 

 becomes the polar nucleus). There will be ten chromosomes at 

 the inner pole of the polar spindle. But if the two lagging chro- 

 mosomes represent a single X chromosome, precociously split in 

 two, there will be nine chromosomes in the outer plate (which be- 

 comes the nucleus of the polar body). There will be as before 

 ten chromosomes at the inner pole of the spindle. Unfortu- 

 nately it is not possible to determine, with certaint}^, whether 

 there are eight or nine chromosomes in the outer plate. I ani 

 inclined, nevertheless, to adopt the former interpretation as the 

 more probable, because of the evidence from P. caryaecaulis 

 that bears on the same point. It will be observed that the end 



