Bilateral Asymmetry in Salmon— -L andrum 
Fig. 1. Supernumerary scale lying on lateral line. 
Occasionally such scales are not penetrated by a lateral 
line canal tube. 
frequently rudimentary. Rudimentary rakers oc- 
curring between the typically uniformly spaced 
rakers (Fig. 2a) and those lying outside the 
main row were not enumerated. Bifurcated or 
branched rakers (Fig. 2b) with a common base 
were counted as one raker. 
Branchiostegal Rays 
All bony elements of the branchiostegal were 
included in counts of this character. In chum 
salmon, particularly, the reduced size and modi- 
fied shape of some anterior rays ( Fig. 3 ) 
resulted in very deceptive radiographic presen- 
tations. In preparation for radiographing, the 
skin and cartilaginous material anterior to these 
rays had to be carefully removed to minimize 
deception. Careful examination was also re- 
quired for recognition of an occasional ray 
which appeared as two rays due to the presence 
of a prominent lengthwise suture. Dissection 
and staining were used to resolve doubtful 
conditions. 
Pectoral Pin Rays 
All fin rays which extended to the basal bones 
of the fin were included in the character. So- 
called "floating rays,” which occurred in various 
positions among the normal rays, were not 
counted (Fig. 4a). No counts were taken from 
fins in which a lateral process arising from one 
position had fused with a process on the op- 
posite side arising either anterior or posterior 
to it. This left both a right and a left side 
process standing alone, as shown in Figure 4b. 
STATISTICAL PROCEDURES 
For each character, the right side counts were 
subtracted from the left side, differences being 
195 
positive when the left side counts exceeded the 
right and negative when the right side counts 
exceeded the left. The significance of the mean 
difference between the number of meristic ele- 
ments in left and right side structures observed 
in each sample was determined using the Stu- 
dent’s t-distribution: 
t = (X — fi)/Sx 
where X equals the mean difference of left side 
counts minus those from the right side, u equals 
zero, and Sx is the standard error of the sample 
mean difference. The hypothesis tested was that 
the difference between left and right side counts 
was zero. The hypothesis was rejected at the 
0.05 level. The probability levels of the ob- 
served t-values are presented in the tables of 
data and results. 
The extent of over-all asymmetry in each char- 
acter was measured by the percentage 100 (L + 
R)/M, and the direction of asymmetry by the 
percentage of sinistrality 100L/(L + R), where 
L equaled the number of specimens with greater 
left side counts, R equaled the number with 
greater right side counts, and N equaled the 
total sample size, including specimens with 
equal numbers of elements in the left and right 
side structures. 
Although there was little or no known bio- 
logical reason to suspect that differential asym- 
metrical development was related to sex or area 
of origin of salmon, these possibilities were ex- 
plored, in so far as the data warranted, for any 
obvious tendencies of this nature. Actual statis- 
FlG. 2. First left gill arch, a, Small raker between 
regularly spaced rakers on ventral arm of the arch; h, 
a bifurcated raker on the ventral arm. 
