Studies on Chromosomes 161 



stricted, assuming the bipartite form in which it enters the equa- 

 torial plate to form the eccentric chromosome. Throughout the 

 growth-period a large plasmosome is also present, usually separate 

 from the chromosome-nucleolus. In properly stained sections 

 these two bodies differ so markedly in staining reactions that they 

 cannot for a moment be confused. In haematoxylin preparations 

 the chromosome-nucleus is intensely black, the plasmosome pale 

 yellowish, bluish or gray. In Montgomery's safranin-gentian 

 preparations (though now somewhat faded) the former is bright 

 red, the latter bluish or nearly colorless. 



There are no females in Montgomery's material; but in view 

 of the relations known in many other related forms it may safely be 

 concluded that the ii-chromosome spermatozoa are female-pro- 

 ducing, and that the female somatic number in this race is 22. 



2 Individuals with twenty-two Chromosomes in the somatic Groups 

 of both Sexes including a pair of unequal 1 dio chromosomes in 

 the Male, and a Pair of equal large ones in the Female 



This condition has been found in seven males and four females, 

 all three species being represented. The three species closely 

 agree in all the phenomena. 



To the males of this type precisely the same description applies 

 as to the foregoing case except that a small idiochromosome is 

 present in addition to the "odd" or "accessory" chromosome. 

 The latter is now indistinguishable from a "large idiochromosome, " 

 and the identity of these two forms of chromosomes, on which I 

 have laid stress in former papers, is thus fully demonstrated. This 

 appears most clearly in the maturation divisions. In the first 

 division the chromosomes show the same grouping as in the 21- 

 chromosome forms, but a small idiochromosome accompanies 

 the "accessory," frequently lying beside it outside the principal 

 ring, though sometimes being in or inside the latter (Fig. 4, a-/, 

 Photos 2, 3). This chromosome is always recognizable as the 

 smallest of all the chromosomes except the m-chromosomes, and it 

 is in general about half the size of the large idiochromosome or 

 slightly less. All the chromosomes now divide equally (Fig. 4, /, 



