EDITH PINNEV. 



I'.altzer has suggested thai tin- hook i> a ] >luri\ alent element 

 composed of two chromosomes united at their polar ends. Ad- 

 mit i in- such an interpretation it -till remains probable that 

 Hipponoe cannot be inclii(k'd in the above series since it was 

 impossible to rind for the long arm of the hook of some eggs a 

 corresponding pair of equal rods in others. The long rods of 

 Toxopiiciistes are so conspicuous in late anaphases that it seems 

 ,i- though the presence of a similar pair in Hipponoe could not 

 be a matter of dispute. Figs. 19, 20 and 21 show anaphases 

 of Toxopiu'iistes containing the characteristic long rods. These 

 Toxopneitxtcs roil- are slightly longer than the long arm of the 

 hook and the 'groups to which they belong arc perhaps not so 

 compact as daughter groups in Hipponoe. 



With Baltzer's suggestion under consideration the question 

 .irises as to whether the V's which resemble the hook in all respects 

 but length of arms are also to be regarded as multiple chromo- 

 somes. If so the method of grouping in Hipponoe differs from 

 anything previously described. 



The idea that the heterochromosome is associated with the 

 inheritance of sex is a point of common consideration when 

 treating of this differential element. 



From the experimental evidence as to the inheritance of sex 

 Castle, '09, has concluded that femaleness depends upon the 

 presence of some factor wanting in the male, the differential 

 factor. Two classes of female zygotes are recognized in CastUV 

 scheme, one, class A in which "femaleness is attained only win n 

 the differential factor is doubly represented in the individual" 

 and another, class B, in which femaleness is attained whenever 

 the dittereiitial factor is present in one only of the conjugating 

 -ametes which produce the individual." The former for which 

 Wilson gives the sex formulas; XX female and X : - male, 

 X in thU case designating the differential factor, is represented 

 by the insects. Castle says, "Direct cytological evidence of the 

 existence of class B is not known at present." The formulas, 

 X< ) - female and ()= male einl iod\ ( 'axle's idea. 



IlippnntK- falls into class A only upon the assumption that the 

 1 look is a multiple chromosome, the Ion- arm hein- the differential 

 element, and that there exists in one-half of the fertilized eggs a 



