228 KATHARINE FOOT AND E. C. STROBELL. 



such complete dissociation do however occur and are shown, for 

 example, in photos 13 and 14, which have the length of intro- 

 mittent organ characteristic of E. variolarius (85-5 mm. and 99 

 mm.) while the specimens from which these organs were dissected 

 have the E. servus absence of spot. Photo 15 has a length of 

 intromittent organ almost equal to E. servus (140 mm.), while 

 the specimen from which this was dissected has the genital spot 

 distinctive of E. variolarius. There are, however, instances of 

 association in the inheritance of the two characters, the intro- 

 mittent organ and genital spot typical of one of the species occur- 

 ring in the same F 2 individual; but exact classification of the 

 full results shows that the two characters are transmitted quite 

 independently of each other. The intermediates, having a large 

 range of variation, make it possible for many of them to appear 

 to show the two characters in the association that would be in 

 harmony with the chromosome hypothesis, but an exact com- 

 parison shows that two plus and two minus intermediates are 

 quite as frequently associated as are a plus and a minus inter- 

 mediate. If we find such independence in the transmission of 

 the two characters, there seems no logical reason for assuming 

 that their factors are carried by the same chromosome. If their 

 frequent independence in transmission forces us to locate them 

 in at least two of the seven chromosomes contributed by each 

 parent, there seems no adequate reason for confining them to the 

 chromosomes at all, especially as their final mode of expression 

 is not dependent upon the distribution at mitosis of unit factors 

 carried by the chromosomes, but upon hypothetical factors 

 outside the chromosomes. 



As the advocates of the sex-determination theory may dismiss 

 these results as in the case of the genital spot on the ground 

 that the intromittent organ is not sex-linked, and is merely a 

 secondary sexual character, it may be profitable to attempt to 

 follow theoretically the transmission of what must be admitted 

 are primary sexual organs, (the ovaries and the testes), while 

 assuming that they are "sex-linked." This has its difficulties 

 in the case of the testes, for the factors determining the sex- 

 linked characters of authors are assumed to be in the chromosome 

 which is homozygous in one sex and heterozygous in the other 



