Cliromatin as "'Ilcrcditarij Substance"* 351 



was obtained by a comparative study of tlic cliromosoiual 

 number and cliaractcr in the Ixxly cells as well as in tlie 

 germ-cells of botli males and females. Miss Stevens's state- 

 ment of results may be given. Refenlnir to Hie |ir(\i()us 

 investigations by herself and Wilson on a considerable list 

 of species of insects belonging to the orders al)ovo men- 

 tioned, she said that in all cases where an odd ciiromosome 

 occurs in the male germ-cells, a pair of such chr(nnosomes 

 occurs in the body cells of the female; from which the con- 

 clusion follows that an vgg fertilized l)y a spermatozoan 

 containing an odd chromosome must produce a female in- 

 sect. 



But a variation from this scheme was found wiiieh, thoui^li 

 not contradictory to the principle involved, made it neces- 

 sary to give this chromosome some other designation. I'he 

 designation chosen by Wilson was X-chromosome, or as 

 later observations seemed to justify, sex chromosome. "X- 

 chromosome" is then, essentially synonymous with '"acces- 

 sory chromosome," and "Y-chromosome" refers to a 

 chromosome in some species as a mate to the X-chromosome. 

 But since the Y-chromosome constitutes a further compli- 

 cation, though not a fundamental modification of the prin- 

 ciple of the relation of chromosomes to sex, the ])urpose of 

 this discussion would not be furthered hy going into the 

 subject in more detail, interesting as it is from various otiier 

 standpoints. 



The other kind of evidence which we will mention con- 

 necting sex with chromosomes has come from animals which, 

 like some bees and wasps, propagate by fertilized virirs i)art 

 of the time and by unfertilized or virgin or parthenogenetie 

 eggs the rest of the time. As soon as the fact had Ix-en 

 discovered that a chromosomal difference between the two 

 sexes occurs in some animals which always reproduce bl- 

 sexually, the likelihood of a difference between tin chromo- 

 somes of parthcnogenetically produced females, ordinary 



