12 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



X chromosome is simply an odd chromosome : that if one 

 member of any pair of chromosomes be lost, or degenerate, 

 during the history of a species, the remaining one would be 

 the X chromosome, with all its known relations to sex : that, 

 in fact, the X chromosome has no more vital connection with 

 sex than any odd chromosome might have. The X chromo- 

 somes are not sharply distinguished from the autosomes by 

 size or shape : they are often larger than the rest, but by no 

 means always so. Usually they are most clearly distin- 

 guishable during cell division, and then their whole behaviour 

 suggests lack of activity rather than special function. They 

 seem to have fallen out of line as it were, remaining inactive 

 while the rest go through the complicated changes prior to 

 syndesis, and lagging behind on the spindle during anaphase, 

 sometimes even being left out of the daughter nuclei altogether 

 as in Rhabdonema. The fact that in many species one member 

 of the abnormal pair is altogether lost, while in others, although 

 present, it behaves in regard to Mendelian inheritance as 

 though it carries no factors, all seem to point to a condition 

 of degeneracy. Also Morgan and Bridges 26 have recently 

 shown that non-disjunction appears to take place more often 

 in the X chromosomes than in the autosomes ; and if this be 

 true it again points to lack of normal activity In fact, if any 

 pair of chromosomes began to take a less active part in the 

 total metabolism, they could give the complete cytological 

 phenomena associated with the X chromosome. They might 

 also have the observed distribution in regard to the two sexes, 

 as outlined above. The facts of sex-linked inheritance would 

 then follow whichever chromosomes happened to become 

 the ' X chromosomes. Morgan has recently reported an 

 interesting fact. In Nature, February 23rd, 1922, he writes : 

 " Complete triploid individuals having three of each kind of 

 chromosome, have recently been found by Bridges. . . . 

 Their eggs, as shown by genetic tests, contain all possible 



