560 CLARENCE E. McCLUNG 



may not be a multiple. In Mermiria, in the same chromosome 

 of the first spermatocyte, we have two such V's, one of which is 

 multiple, the other not. In Trimerotropis double V's are nu- 

 merous although the complex is not reduced in number. But 

 the form of the chromosome, taken in connection with the 

 number in the complex, the relative sizes of the elements, their 

 structure and beha\aor, is important. With these Umitations 

 on the value of chromosome form in mind, I wish to consider the 

 evidence they afford regarding the nature of the Stenobothrus 

 type of rings and V's in H. viridis. 



In such a study the occurrence of the incomplete ring is very 

 helpful because it constitutes an intermediate form between the 

 two rod condition and the rmg. An examination of these ele- 

 ments in classes 4, 5 and 6 (plate 2) will demonstrate these rela- 

 tions. In the last class, chromosomes 9 and 10 are rods ar- 

 ranged on the spindle parahel with its axis, and there divide at 

 the middle constrictions. Similar structural conditions pre- 

 vail in class 4, ^\dth the exception that, in place of chromosomes 

 9 and 10 as free elements, their position in the size series is occu- 

 pied by a single chromosome in the form of a V placed in the 

 same relation to the spindle. Upon division, the elements of this 

 unusual chromosome separate at their middle constrictions just 

 as did free chromosomes 9 and 10, and in one of the anaphase 

 groups exactly the same conditions obtain as in cells of class 6 

 (fig. 28, pi. 5). The other group has, in place of two rods, a 

 double V corresponding in the number and size of its subdivisions 

 to the sum of those in the two rods from which it separated. All 

 the circumstances of the case indicate that the only unusual con- 

 dition here is the union of chromosomes 9 and 10 at one end, 

 producing, in the diploid condition, a V, whose arms are unequal 

 in size and othermse non-homologous. The origin of such a 

 combination has not yet been determined, but it is not a tempo- 

 rary condition during the m.aturation period, for it is found in all 

 generations of the cells and is undoubtedly present in the so- 

 matic cells. Since it is present in half of the sperm it may 

 as readily perpetuate itself as the two rod condition. If like 

 relations exist during the maturation of the egg, then a means 



