CROSSING TWO HEMIPTEROUS SPECIES. 233 



the male-producing spermatozoa cannot transmit exclusively 

 female characters. That exclusively female characters and 

 exclusively male characters should have such a different mode of 

 transmission does not appear to us to be a logical conclusion, but 

 it is a question that it is possible to put to the test of experiment. 



The point of view of the investigator as to the chromosome 

 theory of sex-determination seems to be entirely dependent upon 

 the extent of his belief in the individuality of the chromosomes. 

 In these insects, for example, the so-called male-producing 

 spermatozoa have the Y-chromosome and not the X-chromosome, 

 and those who believe in such a degree of individuality of the 

 chromosomes as is demanded by the chromosome hypothesis of 

 sex-determination, must hold that a so-called male-producing 

 spermatozoon must develop into a pronucleus with a Y-chromo- 

 some and never an X-chromosome. They must hold that the 

 Y- and X-chromosomes are as individual as the king and queen 

 of chess for example. 



On the other hand, the cytologist who believes that the 

 chromosomes, like other organs in the cell, are the expression 

 rather than the cause of cell activities, can also believe that there 

 are forces outside the chromosomes that determine whether an 

 egg shall develop into a male or female and can further believe 

 that these forces, acting on the developing pronucleus can cause 

 its chromatin content to develop into the chromosome configura- 

 tion which is demanded by the sex. As it is impossible to follow 

 the metamorphosis of a spermatozoon into a pronucleus, the 

 cytological proof can probably never be achieved; but there is 

 definite evidence that cells which normally produce certain 

 organs, can be forced by experimental manipulation to produce 

 other organs which have quite different functions, and such a 

 change of function must create a corresponding change of struc- 

 ture, not only in the visible final result, but in the initial changes 

 of the cell itself. Thus we believe that the structure of the cell, 

 or any part of the cell is not the determining factor, but is merely 

 an expression of other forces. 



