REPTILIAN SPERMATOGENESIS 311 



Sceloporus, where the testes of four males have been examined 

 (after several fixatives), and in addition the somatic divisions 

 of both male and female embryos. In all favorable cells the 

 number of micro-chromosomes seemed to be ten.^ 



What significance does this sharp separation into two chromo- 

 some groups have? Is this merely a striking incident in the 

 spermatogenesis of lizards, or are the macro- and micro-chromo- 

 somes physiologically unlike? May the micro-chromosomes be, 

 perhaps, degenerating chromosomes which have outlived their 

 usefulness in this ancient group? 



From the evidence at present at hand, it appears that this 

 separation into large and small chromosomes is merely an interest- 

 ing incident of lizard spermatogenesis. This conclusion is based 

 on the following observations: First, in the Teiidae, the size 

 demarcation is not so sharp, the two groups grade into each other. 

 Further, the micro-chromosomes behave as true autosomes, 

 fusing in synapsis and dividing in a regular fashion in maturation. 

 There is no evidence to show that their number is variable within 

 the species. It is very probable that in the macro- and micro- 

 chromosomes we are dealing simply with larger and smaller 

 aggregations of chromatin matter.^ 



3. Chromosomes and taxonomy 



In the family Iguanidae, where the spermatogenesis of six 

 species of lizards has been studied, we have, as far as the macro- 

 or large chromosomes are concerned, a confirmation of the general 

 position taken by McClung ('05, '08) after his extensive studies 

 of orthopteran chromosomes, that there is a definite relation 

 between taxonomy and chromosomes ; that the degree of relation- 

 ship may be recognized in the germ-cells as well as in external 

 characters. Robertson ('16) has recently given extensive con- 

 firmation to this view. 



* It will be understood, however, that there is a considerable chance for error 

 in making micro-chromosome counts, for in addition to a chance hiding under 

 other chromosomes, they tend to disappear on long extraction of the stain. 



* In Drosophila several genes have been found to exist in the small dot-like 

 chromosomes. 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 34, NO. 3 



