ROBERTSON: THE CHROMOSOME COMPLEX. 301 



SYRBULA ADMIKABILIS. 



seem to be indifferent as to whether rings or kidney shapes 

 are formed, but their limbs are usually slender and show that 

 they may bend around to each other easily. The extremely 

 small chromosomes, Nos. 1, 2 and 3, of course cannot form 

 rings, on account of their shortness. Assuming that the di- 

 ameter of the rods or univalent arms forming the chromosome 

 is approximately equal for most of the chromosomes, the large 

 chromosomes would then have a tendency to form rings be- 

 cause their limbs are long; the small one to form rods, and 

 especially straight rods, because their limbs are short; and 

 those that come between to form bent rods, V's and rings in- 

 differently because their limbs are either too short always to 

 insure rings or too long always to form rods. The question 

 then as to whether a chromosome shall be a ring or not may 

 be considered as depending in a general way upon the relation 

 existing between the length of its limbs or arms and their 

 diameter. Assuming, as we did, that this diameter tends to 

 remain a constant, the chief determining condition would then 

 be size, and we know the size relation in a chromosome is a 

 constant, therefore the form which is dependent upon size 

 would tend to be a constant. But it is not essential that these 

 chromosomes shall always form rings or not, for the truth of 

 the matter is that they are not always constant in this respect. 

 Undoubtedly other agencies enter in to modify this secondary 

 character, such as condition of the cytoplasm, position of the 

 cell in the cyst, the degree to which the gliding of the chro- 

 matids had advanced in the tetrad before the condensation 

 process of the metaphase had overtaken it. In respect to the 

 cross form it may here be said that the fact that a chromosome 

 appears as such is of no special importance in individuality, 

 for, as has been already shown in this paper, all the ordinary 

 chromosomes pass through this condition. It too may be con- 

 sidered of secondary importance. Many of these agencies 

 thus working together no doubt prevent the chromosomes from 

 doing exactly as they would otherwise do; and if such be the 

 case it would only be that much more proof that the form of a 

 chromosome is not a first essential, not an entirely reliable 

 character upon which to judge individuality. These external 

 conditions, however, do not alter the size relations of the chro- 

 mosomes. That remains a constant under all circumstances. 

 It seems fair to conclude, therefore, that form, though it ought 



