REPTILIAN SPERMATOGENESIS 305 



experience, noted by many observers and found in the lizards, 

 that vertebrate chromosomes are variable in the time at which 

 they di\dde; this may be early or late, each body acting more or 

 less as an independent entity. The result is that while a chro- 

 mosome lying outside of the equatorial plane may be a sex- 

 chromosome, it may also be half of a tetrad which has divided, 

 the other half remaining in the equatorial "plane, or it may be 

 simply some chromosome displaced mechanically, either by the 

 preserving fluids and subsequent treatment or by the sectioning 

 razor. When the number of chromosomes in the spindle is 

 large, so that one cannot identify each one of them in side view, 

 then he can never be sure which phenomena he is observing. 



Because of the peculiar form of the chromosomes in the family 

 Iguanidae, these lizards have been extremely favorable for chro- 

 mosome study. The total number of chromosomes in this family 

 is large, but, happily, the macro-chromosomes, to which the 

 X-chromosome plainly belongs, are small in number (twelve in 

 the spermatogonia and six in the first maturation division). 

 In side views of practically every complete maturation spindle, 

 all of the large elements can be readily seen and three or four of 

 them identified by their size and shape. (This applies to the 

 'a,' 'b,' and *c' chromosomes and the X-chromosome.) During 

 the course of this study, the author has observed, at one time or 

 another, every one of the chromosomes besides the accessory so 

 displaced as to appear to be passing to one pole of the cell undi- 

 vided. Repeatedly cells have been found in which one of the 

 tetrads has divided early, with one half of it lying well 

 towards one pole while the other half was still to be seen in the 

 equatorial plane. (This was often true of the small 'b' chro- 

 mosome.) Such observations emphasize the necessity of check- 

 ing up conclusions made on the first maturation spindle, in 

 order to be sure that a real sex-chromosome has been found. 



There are, of course, five points which should be determined 

 in order to be sure of this. They are: a) the diploid number 

 of chromosomes for the male; b) the haploid number of chromo- 

 somes in the first division and their behavior; c) the number 

 of chromosomes present in the second spermatocytes; d) the 



