INTRODUCTION. 9. 



serpents, lizards, turtles, crocodiles, and frogs ; and, like Aristotle, 

 he called the four latter " oviparous quadrupeds.'' Lipnseus called 

 all reptiles " Amphibious animals," but the study of the frog 

 family, and the fact that they begin life like a fish, breathing through 

 gills, has caused them to be separated from the class Reptilia- 

 and formed into a distinct class, the Batrachia, from fSmoyps, a 

 frog. They include a great many species in different parts of the 

 world, while those at home are confined to frogs, toads, and their 

 relatives the newts. Batrachians are true Amphibians, living alter- 

 nately both in water and on land. 



It is quite worth the attention of students to compare the- 

 progressive systems of some of our best-known naturalists. A 

 general comprehension of the animal kingdom may be thus, 

 obtained ; and a knowledge of the terms most frequently employed 

 will be of use in whichever branch he desires to study. 



Aristotle divided living beings into eight groups ; viz. — 



Those with Blood. 



1. Viviparous four-footed animals; 2. Birds; 3. Oviparous- 

 four-footed animals ; 4. Fishes. 



Those without Blood. 



5. Soft animals (Cephalopods, etc.) ; 6. Soft animals with 

 shells (Mollusca) ; 7. Insects ; 8. Shelled animals, 

 (echini, snails, and mussels, etc.). 



For a long while, in classifying "reptiles'' and insects much 

 confusion prevailed. The latter were "serpentes " because they 

 creep ; while the former were sometimes called " insects," because- 

 they lay eggs. It is not uncommon even now for the uneducated, 

 to speak of small reptiles as " insects." 



Regarding classification Cuvier wrote — " It will be found that 

 there exist four prindipal forms, four general plans on which alL 

 animals seem to have been modelled ; " viz. — 



1, Animalia vertebrata ; 2. Animalia mollusca; 3. Animalia- 

 articulata ; 4. Animalia radiata. 



The last named is designated by Owen " a chaotic group," and 

 by Huxley a " radiate mob ; " but even now, as the microscope- 

 reveals fresh organisms and unsuspected relationships, zoologists- 

 differ in the arrangement of these sub-kingdoms. It must not 

 be thought, therefore, that in criticising the classifications of those- 

 great men who may be termed the Fathers of Zoology, any slur is- 

 cast upon their work. In the labour of their lives they achieved 

 results which have been starting-points for their successors- 



