312 THEOPHILUS S. PAINTER 



Among all the Iguanids studied, the number of macro-chromo- 

 somes (involving considerably over 90 per cent of the chromatin 

 matter) is always the same, namely, twelve, and, what is more 

 remarkable, these chromosomes show the same size relations. 

 There are always, in the spermatogonia, the pair of large 'a,' 

 the small 'b,' and the intermediate 'c' chromosomes (see figures 

 as follows: Anolis, figs, 1, 2, 3; Sceloporus spinosus, figs. 25, 26, 

 27; Sceloporus U. consobrinus, text fig. 1, A; Holbrookia texana, 

 fig. 37; Uta ornata, text fig. 2, A and B; Crotophytus text, 

 fig. 3, A). The six remaining chromosomes are too much the 

 same size and shape to allow one to pair up accurately synaptic 

 mates. So similar are the macro-chromosomes, of these six 

 species that, except for the micro-chromosomes, the cell plate 

 of one form might be easily substituted for another without 

 its being detected. 



On the other hand, the micro-chromosomes, representing in 

 the aggregate less than 10 per cent of the chromatin, do not show 

 this constancy in size and number The number varies from ten 

 to twenty-two, and even in closely related species, as Sceloporus 

 spinosus and S. U. consobrinus, we have ten and eighteen, 

 respectively, in the germ cells. Why should the macro-chro- 

 mosome be so constant in size and number and the micro-chro- 

 mosomes so variable? Two possibilities suggest themselves. 

 One is, that in hzards we are witnessing the formation of a small 

 number of large chromosomes through the fusion of the small 

 bodies with the macro-chromosomes, and that this process has 

 gone on in different degrees in different lizards. The other is 

 that while the mass of the micro-chromosomes remains the same 

 throughout the family, there is a tendency in different species for 

 these bodies to fuse together into compound bodies. The 

 latter possibility receives some support from the observation that 

 in somatic divisions these micro-chromosomes do unite, and 

 further, where we have a small number of micro-chromosomes, 

 as in Sceloporus spinosus, they are relatively large in individual 

 size, while when they are numerous, as in Sceloporus U. conso- 

 brinus, they are relatively smaller. (Compare micro-chromo- 

 somes of figs. 25, 26, 27 with small bodies in text fig. 1, A.) 



