118 THE HISTORY OF CREATION. 
Linneus. The artificial system differs essentially from the 
natural one, in the fact that it does not make the whole 
organization and the internal structure (depending upon the 
blood relationship) the basis of classification, but only 
employs individual, and for the most part external, charac- 
teristics, which readily strike the eye. Thus Linnzus dis- 
tinguished his twenty-four classes of the vegetable kingdom 
principally by the number, formation, and combination of 
the stamens. In like manner he distinguished six classes 
in the animal kingdom principally by the nature of the 
heart and blood. These six classes were: (1) Mammals; 
(2) Birds ; (3) Amphibious Animals ; (4) Fishes ; (5) Insects ; 
and (6) Worms. 
But these six animal classes of Linnzeus are by no means 
of equal value, and it was an important advance when, at 
the end of the last century, Lamarck comprised the first 
four classes as vertebrate animals (Vertebrata), and put them 
in contrast with the remaining animals (the insects and 
worms of Linnzeus), of which he made a second main division 
—_the invertebrate animals (Invertebrata). In reality Lamarck 
thus agreed with Aristotle, the father of Natural History, 
who had distinguished these two main groups, and called 
the former blood-bearing animals, the latter bloodless 
animals. 
The next important progress towards a natural system of 
the animal kingdom was made some decades later by two 
most illustrious zoologists, Carl Ernst Bar and George Cuvier. 
As has already been remarked, they established, almost 
simultaneously and independently of one another, the pro- 
position that it was necessary to distinguish several com- 
pletely distinct main groups in the animal kingdom, each of 
