209 
next lower number, 15, while only 4.80% have the next higher number, 17. Sim- 
ilarly, in the females, 42%, have 15 and only 5.60% have 17. While therefore the 
per cent. of specimens possessing a given number of rays may differ slightly in 
the two sexes, this slight dissimilarity is lost to a very large extent in the much 
more striking correspondence of the nature of the variation of the two sexes. 
3. The males are more variable than the females. Recently the method of 
using the average deviation of each specimen from the mean as an index of varia- 
bility, has come into vogue. While this method tells really nothing of the extent 
of variation from the mean, the symmetry or asymmetry of variation or of in- 
stances of great variability, it is of interest in permitting a comparison between 
two groups of individuals to be expressed numerically, a method more striking to 
a hasty glance than the parallel columns of the tables. Compared in this way, it 
is found in Table I that the males have usually a greater index of variability than 
the females, the only exception in Table I being in the specimens ’95°._ Arrang- 
ing these indices of variability, we find the variability of the males and females 
to be to each other as 5073:4680. The means were here calculated to two dec- 
imals only, so that a slight error is usually present in the index of variability of 
the males and females combined, as given in the third series of columns, and the 
indices of variability of the males and females separately. Averaging the per 
cents. of specimens having the highest prevailing. number in the fins, we find that 
on an average 1.1 per cent. more females have the prevailing number than males. 
14—ScrencE. 
