CLASSIFICATION OF ACTINIARIA 567 
with. Omitting for the sake of brevity any criticism of existing 
classifications, and regarding Actiniaria as an unclassified 
series, it may then be inquired what method can be applied 
to them to find out their inter-relations. Clearly unit characters 
are not much help, since they may vary independently, and may 
enter into combination in different genera with various sets 
of others. It is therefore necessary to sum up the chief features 
of each genus, and to see which genera have most in common 
with which others ; and those sharing most can be united in 
families. The result is a natural grouping, and one which 
expresses relationships of animals as wholes, and not analogies 
of isolated parts of their bodies. The classifications of Lamelli- 
branch Mollusca may be referred to as an example of several 
overlapping schemes affecting the same group, founded on 
few characters, and each expressing the relationships and evolu- 
tion of one set of anatomical details (be it siphons and pallial 
lines, hinge lines and teeth, adductor muscles, or gills), and not 
expressing those of Lamellibranch animals as wholes. 
It is found, however, that after applying the method of 
summation of characters, families can be defined by 
half a dozen or more common features, and may form so graded 
a series that there are only unit-differences between some of 
them. On the other basis there were sometimes only single 
or few differential resemblances between the members of 
a family, accompanied by important differences. To look at 
it from another angle, it has been said that criticism is finding 
out why one likes or does not like a given book or picture. 
It seems fair to say that classification is finding out why 
a horse is more like a mule than like a wolf—we know instine- 
tively that it is so, but if we can confirm that instinct by good 
reasons we have a classification. Similarly, given enough 
study of a group, and enough training of the relationship- 
instinct, it is felt that from their whole organism and make-up 
certain forms are more nearly related to some of their brethren 
than to others. This may be of very great help, but of course 
needs cautious exercise and confirmation. The point is that 
the principle of summation of chief characters gives this 
