88 Edmund B. Wilson 



ciated to form a definite pentad element of which four pass to one 

 pole, one to the other, while the remaining fifteen chromosomes 

 divide equally. Half the spermatozoa thus receive sixteen chro- 

 mosomes and half nineteen. From these facts it is clear that the 

 sixteen-chromosome class must be male producing, the nineteen- 

 chromosome class female producing, according to the formula : 



GALGULUS 



Egg ^ + spermatozoon^ "~ 3 ~ zygote « — 3 (c?) 

 Egg ^_ + spermatozoon " = zygote « ( 9) 



This case, together with that of Syromastes (if my inference regard- 

 ing this form be correct) shows that we must considerably enlarge 

 our previous conceptions as to the relations between sex produc- 

 tion and the chromosomes; for we can no longer hold that only a 

 single pair are involved. In Syromastes there are two such pairs, 

 in Galgulus several pairs. 



A COMPARATIVE REVIEW OF THE TYPES OF SEXUAL DIFFERENCES 

 OF THE CHROMOSOMES 



It is evident that a greater variety of types exists in regard to 

 the sex differences than was indicated in the brief general review 

 given in the third of my "Studies" (Wilson '06.) In that paper 

 I distinguished three types, examples of which are given by 

 Protenor, Lygaeus and Nezara; but the number must now be 

 increased to at least five, and possibly to seven, of which I will 

 now give a brief synopsis. With the exception of Syromastes 

 and Diabrotica this synopsis includes only species of which both 

 sexes have been accurately determined. Forms like the aphids, 

 in which idiochromosomes have not yet been positively identified, 

 have been omitted. Seventeen of the species are here reported 

 for the first time (one or both sexes) from my own results hitherto 

 unpublished. I am indebted to Dr. Stevens for permission to 

 include her results on the Diptera and on Diabrotica, which are 

 now in press ('08a, '08b). 



