310 THEOPHILUS S. PAINTER 



fifty-six, and in very few instances was any author quite certain 

 of his count. An error of one chromosome is not improbable. 

 The author is of the opinion that when the common vertebrates 

 are restudied with improved technique, it will be found that the 

 bipartite X-element arises from two spermatogonia! chromo- 

 somes, and that its bipartite form during the first maturation 

 division is an expression of this bivalency, and not the precocious 

 appearance of the plane where the second maturation spindle will 

 separate these elements. 



2. Morphology of chromosomes in lizards 



A very striking and interesting feature of the morphology of 

 the chromosomes among lizards is the sharp separation into two 

 size groups, which I have termed, for convenience in description, 

 macro- and micro-chromosomes. This size relation, most con- 

 spicuous among the Iguanidae, is constant throughout matura- 

 tion and in somatic divisions, although, as I have noted several 

 times in this paper, there is some tendency for several micro- 

 chromosomes to become associated together to form long thin 

 rods. 



The macro-chromosomes appear in somatic and spermato- 

 gonia! divisions typically as equal-armed V- or U-shaped bodies. 

 These are really ' bent-rod' chromosomes, as defined by Robertson 

 ('16, p. 221), since there is typically no achromatic bridge between 

 the two halves. In the first maturation division these macro- 

 chromosomes form tetrads (except the X-element) with usually 

 a ring or a double-cross form. In the second division we find 

 bent rods or open V-shaped bodies going to either pole. 



The micro-chromosomes appear typically as rounded dots in 

 spermatogonia! and maturation divisions, but in somatic 

 divisions they may be elongated, short rods, or rarely small 

 V's being formed. These small bodies unite during synap- 

 sis, so that bilobed or bipartite masses are found in maturation. 

 All micro-chromosomes divide in a regular fashion and, as far 

 as I can determine, the spermatids all receive the same number 

 of them. Furthermore, their number seems to be constant in 

 different individuals. This has been most carefully studied in 



