REPTILIAN SPERMATOGENESIS 309 



points have been tabulated for all cases of vertebrates where the 

 sex-chromosomes have been seen in maturation spindles: first, 

 the number of spermatogonial chromosomes going to make up 

 the sex-chromosome; second, the appearance of the X-chromo- 

 somes in the maturation spindles, and, third, the behavior of 

 the X-chromosome. 



A glance at column 3 of this table will show that the first 

 maturation division has been reported as the reductional division 

 in nineteen out of twenty cases (the exception is Yocum's work 

 on the house mouse). In lizards, of course, the X-chromosome 

 does not divide in the first maturation division; hence this is 

 the reduction division, as far as the sex-chromosomes are 

 concerned. 



The second column shows, in the vast majority of cases where 

 we are dealing with the X-condition this chromosome is bipar- 

 tite in form. The exceptions are birds and cases where the 

 X-Y condition prevails. Again, in lizards, we invariably find 

 the bipartite condition. 



In the first column it will be noted that most observers describe 

 the X-element as coming from one spermatogonial chromosome, 

 and regard the bilobed form of the first maturation division as 

 a precocious splitting in preparation for the second maturation 

 division. A few workers describe the X-element as coming 

 from two spermatogonial chromosomes (fowl, man, Guyer; 

 and pig, Wodsedalek) , and this is unquestionably the condition 

 found in all the lizards studied. In lizards of the family Iguani- 

 dae the origin of the X-element from two spermatogonial chro- 

 mosomes could be determined with great certainty; there can 

 be no doubt that there are twelve macro-chromosomes in sperma- 

 togonia and six in primary spermatocytes. One of these six is 

 the sex-chromosome. 



Why should we find such close agreement in the appearance 

 and behavior of the sex-chromosomes in vertebrates, and yet 

 find this striking difference in the origin of the X-element? 

 In this 'connection, it may be pointed out what while the 

 number of chromosomes to be dealt with in lizards is small 

 (twelve), other vertebrates show a range from seventeen to 



