11. C. PUNNETT 
343 
This is doubtless effected by the claspers of the </, powerful intromittent organs 
deeply grooved for the conveyance of the seminal fluid, and armed with strong 
spines. Their structure, taken in conjunction with the absence of an ejaculatory 
apparatus, points to copulation being no momentary action. Now, in several 
specimens oi Spinax, I was able to examine the embryos in a very early condition 
shortly after the appearance of the medullary folds. Such early embryos were 
all at approximately the same stage, a fact which, considered in relation with 
what precedes, points to fertilization by a single cT only. Further reference to 
the low values of the fraternal correlations will be made later. 
Absence of Differential Sex Variability in Mothers. 
Whether $s of a given type tend to produce an excess of either sex is a 
question which the present data allow of an attempt at answering. The $ 
parents were weighted for each character with reference to </ and $ offspring 
separately, and the means and standard deviations of these two sets of weighted 
mothers were calculated. The results are given in Table 9. 
TABLE 9. 
Showing Variability of Mothers weighted for and $ Offspring respectively. 
{Number of ^ Offspring=109 ; number of ? Oflspring= 115.} 
M. 
p. E. M. 
(T 
p. E. a- 
Anterior spine | ^ 
16-284 
16-322 
+ -045 
±-042 
+ -7051 
± -666 
+ -032 
± -030 
Posterior spine | ^ 
41-082 
41-035 
+ -046 
±-043 
+ -718 
± -672 
+ -033 
± -031 
Whole vertebrae | ^ 
45-248 
45-156 
+ -056 
±•051 
+ -867 
± -819 
+ •040 
± ^036 
Half vertebrae | ^ 
39-853 
39-852 
+ •105 
±•109 
+ 1-619 
±1-739 
+ •074 
± •077 
Total segments | ^ 
65-440 
65-365 
05 03 
+ 1-062 
±1-050 
+ -048 
±•046 
The vahies both of the means and of the standard deviations are exceedingly 
close in every case^ Only for the standard deviation of total segments is the 
difference between the $ parents, weighted for and $ offspring respectively, 
greater than twice the P. E. a. The average value of a for the five characters in the 
case of the </s is "994 and for the $s "989. From this it may be fairly concluded 
that the production of an excess either of cT or of $ offspring is not associated 
with any difference of type in the $ parent. 
