REPTILIAN SPERMATOGENESIS 307 



precociously split, so that in equatorial view it is difficult to 

 make counts. One does not know whether one or two chromo- 

 somes are involved. The matter is further complicated by the 

 fact that -the second spermatocyte cells do not preserve well 

 (due perhaps to poor penetration). Under favorable circum- 

 stances, however, either five or six macro-chromosomes were 

 found. Anaphase stages of this division were much clearer 

 for study (because of the chromosome shape) and showed that 

 the spermatids received either five or si^t large chromosomes 

 (figs. 19 to 24, 34 to 36, and 45 to 48). 



Among all members of the family Iguanidae which were 

 studied, there were twelve macro-chromosomes in the spermato- 

 gonia, and six of these large chromosomes in the first maturation 

 spindle. This shows that the bipartite body which acts like 

 a typical X-chromosome is derived from two spermatogonia! 

 chromosomes. Since the male is heterozygous as regards sex, 

 the female must be homozygous and have the two X composition. 

 And since the X-chromosome of the male comes from two 

 sperm atogonial chromosomes, we should expect to find that the 

 females had two more large chromosomes than the males (X = 

 two sperm atogonial chromosomes; 2 X = four spermatogonia! 

 chromosomes) . 



A study of the female chromosome complex was made for 

 Sceloporus spinosus, and while the results with the ovarian 

 tissue were not altogether satisfactory, they indicated that the 

 female has fourteen large chromosomes (the male of this species 

 has twelve) . A study of Sceloporus embryos, however, furnished 

 convincing evidence on this point. As a glance at text figure 

 5 will show, some embryos show constantly two more large V- 

 shaped chromosomes than the others. The embryos with the 

 two extra chromosomes would have become females without 

 doubt. 



With this evidence at hand, we cannot escape the conclusion 

 that a true sex-chromosome has been found in the lizards. This 

 X-chromosome is of the 'double-odd' or the 'double accessory' 

 type; that is, X equals two spermatogonia! chromosomes. 



