194 
CHARLES L. PARMENTER 
However, although the measurements may not meet the above 
criteria in all chromosomes, there are certain cases which do meet 
them definitely, and strongly evidence the existence of pairs. 
This fact, together with the above consideration, makes it 
possible that all the chromosomes are in pairs. 
Furthermore, it may be mentioned here that conditions which 
do not meet the above criteria fall far short of proving that 
pairs do not exist. The possibility still remains that two or 
more pairs may be of equal or nearly equal length. Such a 
condition is known to exist in certain Orthopteran chromosome 
pairs (Carothers, T7, pi. 1, tetrads 7 and 8) where the chromosomes 
are unquestionably known to be paired. 
2. Evidence for the existence of pairs. On plate 9, figures 33 
to 37, are five rows of vertical lines representing the relative 
lengths of the chromosomes of as many cells. The differences 
in the lengths of these lines and also the space between adjacent 
lines represent relative differences in chromosome length. For 
convenience the lines are made twice the length of the chromo¬ 
somes as drawn and the width of the spaces are made eight times 
the difference in length. The lengths of the chromosomes, the 
amounts included for foreshortening, and the form of chromo¬ 
somes for each of these cells are also shown, respectively, in 
figures 27 to 31 and 33 to 37. 
A part of the evidence which these graphs present for the 
existence of pairs is three outstanding characteristics common 
to all of them. First, there is a graded series of chromosome 
lengths from the shortest to the longest; second, there is a 
marked sameness in the relative chromosome lengths of these 
cells which appears in the approximately constant presence of 
groups containing the same chromosome pairs, and, third, a 
similarity of form between homologues. 
The pairs, in accordance with the above criteria, were de¬ 
termined primarily on the basis of chromosome length, supported 
by a comparison of form. The graphs and figures of each com¬ 
plex measured show that certain chromosomes are very probably 
homologues. In other cases a number of chromosomes are so 
nearly of the same length that, according to the criteria, the 
