22 LOTSY, DE CHROMOSOMENGETALLEN DER ORGANISMEN. 
means that in forms possessing such X and Y’s or such X and 
Y complexes we have to deal with the simultaneous presence of 
paired and unpaired chromosomes. 
It is pointed out that such an occurreuce in plants has been 
shown to be due to hybridisation between forms possessing 
different chromosome-numbers. 
It is therefore suggested, that the presence of X and Y com- 
plexes or of single X and Y chromosomes is an indication of 
previous hybridization of forms differing in chromosome-numbers. 
The author is well aware, that this is as yet but a suggestion, 
and the present communication is published with no other object 
than to beg zoologists, to whom apparently this idea has not 
yet occurred, to look at the problem from this point of view and 
to test its applicability. 
It need hardly be pointed out, that if this suggestion should 
prove to be correct, it would give considerable support to the 
view that hybridisation has played on important role in evolution. 
The author wishes to lay stress on the point that the suggested 
origin of the X chromosome and its function are of course two 
very different questions. 


