I6O FERNANDUS PAYNE. 



27 chromosomes. This gives the number relations as we find 

 them at present if the individuals with the original number (26) 

 and the females with 27 disappear. The same explanation holds 

 for the remainder of the types if we assume that the large idio- 

 chromosome breaks up into three or four elements instead of 

 two. Another thing which adds weight to the above interpreta- 

 tion is the fact that the behavior of each of the triad, tetrad and 

 pentad groups, as a whole, is exactly comparable to the behavior 

 of a pair of idiochromosomes. Evidently the original irregu- 

 larity might have first occurred in either sex and have been 

 transferred to the other. This gives another method by which 

 the chromosome number may change during the history of the 

 species. While Metapodius and Diabrotica are species where a 

 change is actually taking place at the present time, the forms 

 described in the present paper (with the exception of Dlplo- 

 codus} show a fixed condition after a change has taken place. 



Sc.v Determination. 



In a preliminary note ( '08) Morgan has given some interesting 

 data in regard to sex determination in phylloxerans, where all 

 the fertilized eggs produce females and where both males and 

 females develop from parthenogenetic eggs. In describing the 

 spermatogenesis he says: <; The reduced number of chromosomes 

 is three. In the first spermatocyte division two of these divide 

 equally, but the third lags behind the others, and finally in the 

 very last stages of this division, it retreats to one of the poles. 

 Thus there are three chromosomes in one of the two daughter 

 cells, and only two in the other. Still more significant is the fact 

 that the cell with the fewer chromosomes is very small : it con- 

 tains very little cytoplasm and subsequently degenerates without 

 forming a spermatozoon. In the second spermatocyte division 

 all three chromosomes of the larger cell divide equally, thus pro- 

 ducing two spermatids with three chromosomes each. These 

 spermatids become spermatozoa. They correspond in their mode 

 of development to the ' female-producing ' spermatozoa of other 

 insects. Hence we can understand why all fertilized eggs be- 

 come females." 



To those who have sought to bring forward a theory of sex 



