Chromatin as '^Hereditary Substance** 351 



was obtained by a c()nn)aratlve study of tlie chromosomal 

 number and cliaractcr in the body .cells as well as in the 

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

 ment of results may be given. Referring to tlie previous 

 investigations by herself and Wilson on a considerable list 

 of species of insects belonging to the orders above men- 

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

 occurs in the male germ-cells, a pair of such chromosomes 

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

 clusion follows that an Qgg fertilized by a spermatozoan 

 containing an odd chromosome must produce a female in- 

 sect. 



But a variation from this scheme was found which, though 

 not contradictory to the principle involved, made it neces- 

 sary to give this cliromosome some other designation. The 

 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 purpose of 

 this discussion would not be furthered by going into the 

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

 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 eggs part 

 of the time and by unfertilized or virgin or parthenogenetic 

 eggs the rest of the time. As soon as the fact had been 

 discovered that a chromosomal difference between the two 

 sexes occurs in some animals which always reproduce bi- 

 sexually, the likelihood of a difference between the chromo- 

 somes of parthenogenetically produced females, ordinary 



