30 INTRODUCTION. 
external form. Even Linn aus himself has declared that a natural 
classification of animals is indicated by their internal structure?. 
But if this natural system were quite perfect, it would not merely 
be a register of animals or a large lexicon, but a true image of the 
-animal kingdom and a short survey of the entire science. The 
more nearly the science approaches this end, the greater will be its 
perfection. 
We must here, in few words, mention some of the systems 
which have been proposed in Zoology. 
Animals may be divided into Classes in different ways, and the 
differences amongst individual zoological systems are very remark- 
able. ARisTorLe divided animals into those that have blood 
(€aa) and those that have not blood (aapa), and distributed these 
two chief divisions into lesser ones. Purny founded his division 
upon the different elements in which animals reside, and distin- 
guished these as Terrestrial, Aquatic, and Volatile animals. It 
would carry us too far from our object to enter more fully into 
these and other early attempts at classification. But we must not 
omit to notice the system of Linn.mus, who threw a new light on 
every department of Natural History?. 
In his primary division of animals Linn#®us was a fol- 
lower of ArisrorLE: he named however those animals which 
ARISTOTLE called bloodless, white-blooded: whilst of the rest the 
blood is red. The basis of his further division is taken from the 
Circulation of the Blood. Here follows a sketch of his system. 
Heart with 2 ventricles and { viviparous...... I. Mammalia. 
2 auricles ; warm,red blood ( oviparous ...... II. Birds. 
Heart with 1 ventricle and , withlungs ..... IIT. Amphibia. 
r auricle ; cold, red blood { withvgills) <.. 27). IV. Fishes. 
Heart with 1 ventricle, no f with antenne.... V. Insects. 
auricle ; cold, white blood with tentacula... VI. Worms. 
1 “Divisio naturalis animalium ab interna structura indicatur.” System. Natur. 
Tom. I. p. 19. Ed. xr. 
2 CaroLus Linnaus, born at Stenbrohult in Southern Sweden, 1707, died 1778. 
Comp. on his momentous life RicHarD PuLTENEY, A general view of the Writings of 
Linneus, 2nd edit. London, 1781. D. H. Srover’s Leben des Ritters Carl von Linné, 
2 Thle. 8. Hamburg, 1792. Lyenhiindiga Anteckningar af Cart LINN&US om sig 
sjelf, med anmerkningar och tilltig. Upsala, 1823. 4to. (this is translated into German: 
C. von Linnk tiber sich selbst, &e.) The first edition of his Systema Nature appeared 
