RESULTS OF CROSSING TWO HEMIPTEROUS SPECIES. 485 



and incidentally it relieves the so-called male- and female-producing 

 spermatozoa as such from the responsibility of deciding the sex, and places it 

 squarely with the egg, for from a so-called male-producing spermatozoon 

 a female can develop if this spermatozoon fertilizes an egg in which both 

 X chromosomes have remained, and again from a so-called female-producino- 

 spermatozoon a male can develop if this spermatozoon fertilizes an eo-o- 

 which has no X chromosome.* 



It is naturally incumbent upon the cytologist who makes assumptions so 

 necessary for the defence of a theory to find some cytological proof of them, 

 and Wilson ('14) has made the interesting announcement that "very recently 

 Bridges has tested his assumption cytologically ". And he adds, " The 

 ■cytological examination has demonstrated that certain females of this race 

 actually possess three of these chromosomes." 



Wilson seems to regard this evidence as quite conclusive proof of Bridges' 

 assumptions and deductions. Those of us, however, who have no such 

 sublime faith in the causal nature of the chromosomes are inclined to suspect 

 that if Bridges had searched with equal ardour for an extra X chromosome 

 in the male cells, he might have found these cells also equipped with an extra 

 X chromosome, as in fact we found to be the case in the spermatogonia of 

 Anasa tristis (Foot and Strobell, '07). In spite of our demonstrating this 

 second X chromosome by photomicrographs, the reality of its presence has 

 been questioned by advocates of the chromosome-theories, for it is obviously 

 an embarrassing factor to the sex-determination hypothesis. 



Further study of the chromosomes of the Hemiptera led us to make the 

 following statement which seems to us to have some bearing on Bridges' 

 recent discovery : — " A careful examination of our preparations makes it 

 possible to select chromosome-groups which exactly fit a given theory, but 

 many groups can also be found that are a serious menace to these theories, 

 while, on the other hand, they present no difficulties to the conception of 

 those who regard the number, size, and form of the chromosomes as inherited 

 ■characters — the expression of cell-activities rather than the cause." 



In our preliminary report (Foot and Strobell, '14 c, pp. 228-31) we showed 

 by an analysis of the chromosomes, based on the hypotheses as to their 

 method of division, that the testis itself can have no closer relation to the 

 so-called sex-deteruiining chromosomes than we have shown to be the case 



* Bridges' assumptious, wlien applied to those forms which have a Y chromosome 

 would seem to relieve this chromosome of any sex-limited function, although in these 

 species it is just as distinctive of the male cells as are the two X chromosomes of the female 

 cells. According to Bridges' hypothesis, some males may be without the Y chromosome 

 while some females have it. The admission that such marked structural changes in the 

 male and female chromosome groups can occur in individuals is in harmony with the belief 

 that the chromosomes, like other structures in the cell, are the expression rather than the 

 cause of cell activities. 



