322 
Merism and Sex in " Spimix Niger 
five characters given (i.e. the characters determined in both embryos and adults) 
in each instance. This gives the following figures : — 
Average value of u for five characters 
adults 1-181 
embryos 1-174 
? adults 1-132 
$ embryos ... ... 1-057 
TABLE 2*. 
Comparison of the Standard Deviation (a) and its Probable Error (p. E. cr) 
between the sexes, and between embryos and adults of each sex. 
S adults 
(100) 
S embryos 
(145) 
? adults 
(163) 
? embryos 
(159) 
Anterior spine 
\ <T 
/I'.E. 
0- 
-670 
± -0.32 
-568 
±•023 
-721 
±-028 
•585 
±•022 
Posterior spine 
( (T 
\V. E. 
•888 
±•042 
•910 
± ^036 
•906 
± -034 
•862 
±•028 
Whole vertebrae ... 
\ " 
\V. E. 
o- 
1147 
± •OSS 
1-319 
± -052 
1-072 
±•040 
1-093 
±-041 
Half vertebrae 
) - 
\V. E. 
<J 
1^901 
±•091 
1-917 
±■076 
1-921 
±•072 
1-702 
±-064 
Total segments 
.( ^ 
\y\ E. 
cr 
1-048 
± -050 
1-154 
±-046 
1041 
± ^039 
1045 
±•039 
First girdle-piercing nerve 
\v. E. 
(T 
•871 
± ^029 
•771 
±•021 
Post-girdle nerves 
\ <^ 
(P. E. 
(7 
•819 
± ^028 
•758 
±•021 
Collector nerves 
! " 
(p. E. 
0- 
•630 
± -021 
•606 
±•017 
(1) Comparison between the adidts. The $s appear to be somewhat more 
variable with regard to the position of the spines and also in the number of 
half vertebrae, though the difference in each case is not significant. For total 
segments the variability is almost the same in each sex. The (/"s are more 
variable for whole vertebrae though here again the difference is not really 
significant. The average variability is practically identical in each case (I'lSl 
for cfs and 1-132 for $s). For characters, however, which involve the position of 
the pelvic girdle and plexus the </s are somewhat more variable than the $s. 
In the case of the 1st g. p. n. the difference is more probably significant ; it may 
be significant for the post-girdle nerves. The smaller difference in the collector 
nerves also points to greater variability. A comparison then of the variability 
in the adults only of each sex seems to point (a) to equality of variability for 
characters involving the spines and vertebral column, and (/3) to greater variability 
* Sheppard's Correction has not been used here. 
