12 EARLY PROGRESS 
different foundations may teach us that every 
structural combination includes certain inherent 
necessities which will bring animals together on 
whatever set of features we try to classify them ; 
so that the division of Aristotle, founded on the 
circulating fluids, or that of Lamarck, founded on 
the absence or presence of a backbone, or that of 
Ehrenberg, founded on the differences of the ner- 
vous system, covers the same ground. Lamarck 
attempted also to make the faculties of animals a 
basis for division among them. But our knowl- 
edge of the psychology of animals is still too 
imperfect to justify any such use of it. His 
divisions into Apathetic, Sensitive, and Intelligent 
animals are entirely theoretical. He places, for 
instance, Fishes and Reptiles among the Intelli- 
gent animals, as distinguished from Crustacea 
and Insects, which he refers to the second division. 
But one would be puzzled to say how the former 
manifest more intelligence than the latter, or why 
the latter should be placed among the Sensitive 
animals. Again, some of the animals that he 
calls Apathetic have been proved by later investi- 
‘ gators to show an affection and care for their 
young, seemingly quite inconsistent with the epi- 
thet he has applied to them. In fact, we know 
so little of the faculties of animals that any classi- 
fication based upon our present information about 
them must be very imperfect. 
