340 Merism and Sex in " Spinax Niger " 
We can of course analyse the existing relationships; we have the following 
tables ; 
Regression Coefficients. 
Gives in 
Change of a unit in 
X 
.'/ 
z 
t 
y 
1 
-•309 
- -450 
-•225 
1 
•068 
-•321 
•066 
1 
•099 
•473 
•428 
The following are the percentage changes in x, y, z : 
Gives percentage 
change in 
Change of 
a unit in 
X 
y 
2 
t 
X 
-1-41 
-2-01 
•62 
y 
-1^26 
+ •a? 
1-93 
-1-84 
+ •as 
These results appear of considerable interest. We see (i) that a gain of one in 
the total segments makes on the average five times as much absolute effect, and 
three times as much percentage effect on the median and posterior as on the 
anterior series : (ii) that a gain in either median or posterior series is accompanied 
by a very small gain in either posterior or median series respectively, but in both 
cases by a sensible loss in the anterior series, (iii) Conversely a gain in the 
anterior series is associated with sensible losses in median and posterior series ; 
and (iv) gains and losses in anterior and posterior series have the highest 
relation, i.e. the loss of a segment in the anterior series is accompanied by a 
considerably greater gain in the posterior series than in the median series, and 
the gain of a segment by a greater loss in the posterior than in the median series. 
This more intimate relation of the extreme series than of either with the median 
series seems of considerable suggestiveness. 
Lastly I have worked out the partial correlation coefficients of the three 
subgroups on the hypothesis that the total number of segments remains constant, 
i.e. expressions like : 
Rxy = {t^ - rMryt)lJO- - - Tyf). 
I find 
Or we find a sensible negative correlation nearly equal to — "5 between all three 
series. That is to say that if individuals of the same number of total segments be 
