966 THE AMERICAN NATURALIST. |. [Vor. XXXIV. 
correlation, I found the correlation between the number of 
hooks and the length of the periphery of the statoblast to be 
r= — .0920+.0055, a very low correlation, but slightly negative. 
I give the correlation surface : 
Xa X II 1a 13 I4 I5 16 17 18 19 
255-59-9 I I 
260-64.9 | 2 I 
265-69.9 | 3 3 E I 
270-74.9 | 4 5 14 I2 » 4 F 
275-79-9 5 I 18 6 2 5 I o I 
280-84.9 | 6 I 3 I5 6 4 3 
285-89.9 | 7 3 o o I 
xd A= 13.8264. xd A = 48182. 
€ = 1.3403. g = 1.0499. 
The negative correlation between length of periphery and 
number of hooks signifies that in the long run small stato- 
blasts tend to have slightly more hooks than large statoblasts, 
a result which we should hardly have anticipated. The result 
makes it clear that the number of hooks which shall develop is 
not determined by the space at their command for development. 
In a statoblast with eleven hooks, these are twice as far apart as 
in a statoblast with twenty-one hooks. The ontogenetic cause of 
the variation in number of folds remains thus still undetermined. 
Although the zumber of hooks is not directly correlated with 
the periphery of the statoblast, it is rather strongly correlated 
with the /ength of the hooks ; and the correlation is inverse. 
This is quite striking from superficial observation. To express 
the relation in a roughly quantitative way, I measured a repre- 
sentative lot of the hooks on each of ten statoblasts. In eight 
statoblasts having thirteen or fourteen hooks the average length 
of the hook was about .22 mm. ; in the two with sixteen hooks 
the average length was .19 mm. The figures of statoblasts 
accompanying this paper will show that at greater extremes 
the difference in the hooks is still greater. 
As the hooks decrease in size with increase in number, we 
might expect to find the hooks very small in the statoblasts 
