CATEGORIES OF CLASSIFICATION. 33 



wherever such a tendency is perceptible in the 

 Radiates it is subordinate to the typical plan on 

 which the whole group is founded. They are 

 spheroidal bodies ; yet, though many of them 

 remind us of a sphere, they are by no means 

 to be compared to a mathematical sphere, but 

 rather to an organic sphere, so l-oaded with life, 

 as it were, as to produce an infinite variety of 

 radiate symmetry. The mathematical sphere 

 has a centre to which every point of the sur- 

 face bears identical relations ; such spheres do 

 not exist in the Animal Kingdom. A sphere 

 of revolution, in consequence of its rotation up- 

 on its axis, presents equally flattened poles with 

 meridians of equal value ; this also is no organic 

 character. A living sphere has unequal poles 

 as well as unequal meridians, however much it 

 may resemble a perfectly spheroidal body, and 

 the whole organization is arranged, not neces- 

 sarily around a centre, but always around a 

 vertical axis, to which the parts bear equal re- 

 lations. 



In Mollusks there is a longitudinal axis and 

 a bilateral symmetry ; but the longitudinal 

 axis in these soft concentrated bodies is not 

 very prominent, except in the highest class ; 

 and though the two ends of this axis are dis- 

 tinct from each other, the difference is not so 

 marked that we can say at once, for all of 



2* C 



