192 
CHARLES L. PARMENTER 
by the first condition, should exceed the errors of measurement 
by a good margin. Unless the above conditions are met, the 
errors of measurement make it possible to contend that the 
chromosomes are arranged in a series of successively increasing 
lengths which bear no relation to one another and therefore do 
not represent pairs. 
In addition to the above, the form of the chromosome, which 
is probably determined in large part by the position of the 
spindle fiber attachment, may be used as an aid in determining 
which chromosomes are homologues. McClung (’14, p. 674) 
pointed out that, although the spindle fiber attachment may be 
different on different chromosomes, nevertheless, for each chro¬ 
mosome “it is most precise and constant” in the individual. 
Carothers (’17, p. 470) has shown that for certain tetrads (e.g., 
figs. 32 and 63) the point of spindle fiber attachment on one 
homologue is different from that on the other. But she also 
finds that the point of fiber attachment is constant on a given 
homologue for each individual. She shows (figs. 32, 32 a and 
63, 63 a) that the point of spindle fiber attachment on these 
homologues in the spermatogonia is preserved in the tetrads. 
However, an exception to constancy of fiber attachment in the 
individual has been noted by Wenrich (’16). He found in a 
rod-shaped tetrad of another genus that the fiber attachment 
might shift from one end of the chromosome to the other in 
certain individuals. Therefore, according to the theory of the 
individuality, in the somatic chromosomes the homologues of 
certain pairs of chromosomes may be expected to be unlike in 
form. However, individuals showing such conditions are very 
few and should be considered exceptions rather than the rule. 
There is the possibility that these heteromorphic homologues 
may not be confined to the Orthoptera, and certain cases in 
Ambystoma make this appear to be so. 
Finally, it would be remarkable if any material satisfied the 
above criterion in all points. The small difference in length 
between some chromosomes makes it impossible to demonstrate 
beyond doubt the presence of pairs among them. Again, the 
possibility that the chromosomes may not condense at equal 
