528 CLARENCE E. McCLUNG 



A discussion of these various classes of complexes will serve 

 to bring out most clearly the conditions prevailing in the species. 

 Of these the first shows no unusual conditions whatever, and had 

 specimens of this nature been the only representatives of the 

 genus examined, they would have been regarded as coming from 

 a group entirely typical of the family. There are the usual 

 twelve chromosomes in the form of rings, V's, crosses and rods 

 as found in Hippiscus, all of the telomitic type. The accessory 

 chromosome is free and early passes undivided to one pole of 

 the spindle. Of thirty-eight individuals studied, five had this 

 chromosome constitution. 



Seven of the thirty-eight belong to the second class and were 

 the only kind of which I had preparations when my first study 

 was made. Conditions here are as in class 1, with the striking 

 exception that the accessory chromosome is joined permanently 

 to one of the tetrads, forming a hexad element. The structure 

 and behavior of this complex of eleven chromosomes instead 

 of twelve, has been fully described and will not need further 

 consideration here. 



Very different is the aspect of the complex in the five indi- 

 viduals in class 3. Instead of twelve separate chromosomes as 

 in class 1, or eleven like class 2 there are but ten. We recog- 

 nize at once the hexad multiple of the second class and, in addi- 

 tion, eight telomitic tetrads of characteristic forms. The tenth 

 element is much the largest and is otherwise strikingly different 

 from its mates. In shape it is a much elongated ring of the 

 Stenobothrus type, but, like the rings of Chloealtis, usually 

 lacking any lateral extensions. Not infrequently there will be a 

 separation on one side of the ring producing a C-shaped structure. 

 The character of this element will be considered later in con- 

 nection with other chromosome forms. 



Members of class 4, of which I have seven indiAdduals, show 

 still further modifications. The number of chromosomes is 

 reduced to nine, among which are distinguishable six tetrads of 

 usual types, two large Stenobothrus rings and a hexad multiple. 

 The two differential rings are of unequal size. The larger is 

 directly comparable to the similar element of class 3, but the 



