INTRODUCTION 5 



these creatures, along with snails, mussels, and the like, in 

 the group Mollusca, and even the great anatomical skill of 

 Cuvier failed to show their true position, which was made out 

 only when Vaughan Thompson, about fifty years ago, proved, 

 from a study of the newly hatched young, that their proper 

 place is among the Crustacea, in company with crabs, 

 shrimps, and water-fleas. 



Given a sound knowledge of the anatomy, histology,. and 

 embryology of animals, their Classification may be attempted 

 — that is, we may proceed to arrange them in groups and 

 sub-groups, each capable of accurate definition. 



The general method of classification employed by zoolo- 

 gists is that introduced by Linnaeus, and may be illustrated 

 by reference to the group of cats which we have already 

 used in the explanation of the terms genus, species, and 

 variety. 



We have seen that the various kinds of true cat — domes- 

 tic cat, lion, tiger, etc. — together constitute the genus 

 Felis. Now there is one member of the cat-tribe, the 

 cheetah, or hunting leopard, which differs from all its allies 

 in having imperfectly retractile claws and certain peculiari- 

 ties in its teeth. It is therefore placed in a distinct genus, 

 Cyncelurus, to mark the fact that the differences separating 

 it from any species of Felis are of a more fundamental char- 

 acter than those separating the species of Felis from one 

 another. 



The nearest allies of the cats are the hyaenas, but the 

 presence of additional teeth and non-retractile claws — to 

 mention only two points — makes the interval between 

 hyaenas and the two genera of cats far greater than that 

 between Felis and Cynaelurus. The varying degree of differ- 

 ence is expressed in classification by placing the hyaenas in 

 a separate family, the Hyiznidiz, while Felis and Cynaelurus 



