TREE-LIKE GROUPING, 35 
tree-like grouping of the members of the same family. 
The reciprocal relations of the various families can- 
not be represented in a simple line; though in former 
days more importance was attributed to the general 
indications of the relative value of the types. On the 
other hand, descriptive zoology had long been compelled 
to devise tables of affinity for the systematic subdivisions, 
descending even to species according to the criterion of 
anatomical perfection ; and these found expression only 
in diagrams of highly ramified trees. Branches ap- 
peared which terminated after a brief extension ; others 
are greatly elongated with numerous side branches; in 
every branch characteristic phenomena and series are 
made manifest. 
Let us attempt it with the Vertebrata, for example. 
Even with the fishes we fall into great perplexity ; 
which to place at the end as being the highest. But 
take which we will, the sharks or, our teleostei, the am- 
phibians cannot be annexed in a direct line, nor does the 
‘elongated branch line of the latter merge, as might be 
imagined, into the reptiles. The birds, on their side, 
offer a sharp contrast to the mammals, and this separa- 
tion and divergence extend to all the subdivisions, We 
must figuratively represent family branches, clusters of 
genera, and tufts of species, which latter ramify into 
sub-species and varieties. With this representation of 
the tree-like distribution of the system, we shall gladly 
revert to the comparison of the members of different 
types, with reference to their functional value. The bee 
in itself is manifestly a far more complex organism than 
the lowest fish-like animal, the lancelet ; and in these two 
we compare a low formof ahigh type, and a high form 
