THE CLASSIFICATION OF ANIMALS. 225 
chasm between Crocodiles and Fishes. Birds seem iso- 
lated; but in ancient times there were flying Reptiles ; 
while the Ornithorhynchus, Kangaroo, and Bat stand on 
the border-line between Mammals and the feathered tribe. 
Even between the grand Vertebrate and Invertebrate di- 
visions there flits a ghost-like form—the Amphioxus, half 
Worm, half Fish. 
We have, then, groups subordinate to groups, and inter- 
locking, but not representing so many successive degrees 
of organization. For, as already intimated, complication 
of structure does not rise in continuous gradation from 
one group to another. Every type starts at a lower point 
than that at which the preceding class closes; so that the 
lines overlap. While one class, as a whole, is higher than 
another, some members of the higher class may be inferi- 
or to some members of the lower one. Thus, certain Star- 
fishes are nobler than certain Mollusks; the Nautilus is 
above the Worm, and the Bee is more worthy than the 
lowest Fish. The groups coalesce by their inferior spe- 
cies; ¢.g., the Fishes do not graduate into Reptiles through 
their higher forms, but the two come closest together low 
down in the scale. Man appears to be the goal of crea- 
tion; but even within the Vertebrate series, every step of 
development, say of the Fish, is away from the goal. The 
highest Fish is the one farthest from Man. 
A number of animals may, therefore, have the same 
grade of development, but conform to entirely different 
types. While a fundamental unity underlies the whole 
Animal Kingdom, suggesting a common starting - point, 
we recognize four or five distinct plans of structure.’ 
Thus, animals like the Coral, unlike all others, have the 
alimentary canal opening into the body -cavity, have no 
separate nervous and vascular regions, and the parts of 
the body radiate from a centre. Such form a subking- 
dom called Celenterata. Animals, like the Star-fish, hav- 
15 
