No. 408.] PECTINATELLA MAGNIFICA. 963 
The curve is of Type IV, or has unlimited range, like most 
biological curves. The skewness of the distribution indicates 
possibly a selective weeding out of statoblasts with a small 
number of hooks. Such a result is not unlikely, for (within 
certain limits) we might expect statoblasts with a larger num- 
ber of hooks to have a better chance of keeping their hold and 
forming new colonies than those with fewer hooks. On the 
Fic. 8. 
Fic. 7. — Early stage in formation of hooks. Section taken in the plane of the float 
and at its outer margin. 
Fic. 8. — Later stage in formation of hooks. Section taken as in Fig. 7. X ca. 400. 
other hand, the skewness may mean a tendency of the species 
to give rise to races with a larger modal number of hooks than 
13. Sucha race has been formed in Maine (Hyatt) ; and in 
P. gelatinosa the number of hooks is said to be “ great " (Oka). 
We have next to consider the question whether there is an 
hereditary tendency to produce a certain constant number of 
of variation, and it is doubtless to be preferred to the coefficient. In the remain- 
ing cases, which are graduated variates, the coefficients are the more constant, 
varying from 4 to 9, whereas the indices vary from 2 to 23. Doubtless here the 
coefficient is to be preferred; moreover it is an abstract number, so that the 
results are comparable, whether millimeters, inches, degrees, or percentages are 
mployed as units of measurement. 
