302 J. E. WODSEDALEK. 



while the female cells contain two, making a total of thirty-seven 

 in the male and thirty-eight in the female. These numbers 

 correspond exactly with those of the spermatogonia in the male 

 and the oogonia in the female. This is very significant in relation 

 to our chromosome theory of sex-determination. 



VIII. SEX-CHROMOSOMES IN RELATION TO SEX-DETERMINATION. 



It was shown that in the process of spermatogenesis two distinct 

 types of spermatozoa are produced of exactly the same number. 

 The one type contains eighteen ordinary chromosomes plus one 

 Sex-chromosome, and the other type contains only the eighteen 

 ordinary chromosomes; this being the result of the unequal 

 primary spermatocyte division, where the eighteen bivalent 

 chromosomes divide and the unpaired sex-chromosome passes 

 over to one pole undivided. In the oogonia there are thirty-six 

 ordinary chromosomes plus two sex-chromosomes. Before the 

 reduction division of the primary oocytes, in all probability 

 (though this was not actually determined in this animal), all of 

 the chromosomes, including the two sex-chromosomes, pair. 

 This eventually gives rise to ova all of which contain the reduced 

 number of chromosomes or eighteen ordinary chromosomes plus 

 one sex-chromosome. 



Since the two types of spermatozoa are produced in equal 

 numbers, fertilization by the one kind or the other is equally 

 possible, and the number of male and female calves born is about 

 equal if a fairly large number of offspring is considered. Sex 

 in the offspring, as determined at the time of fertilization of the 

 ovum by the one or the other type of spermatozoon may be 

 illustrated as follows: 



Spermatozoa. Ova. Offspring. 



(18 + i) + (18 + i) = (36 + 2) = female, 

 (18 + o) + (18 + i) = (36 + i) = male. 



The results of the above combinations are in exact accord 

 with the number of chromosomes found in the germinal and 

 somatic cells of the two sexes in cattle; and the relation of the 

 sex-chromosomes to sex-determination can not be doubted. All 

 of the five hundred or more so-called theories or rules for con- 



