INTRODUCTION. 9 



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

 he called the four latter "oviparous quadrupeds." Linnaeus 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 ySara^os, 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. 



i. 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 u It will be found that 

 there exist four principal forms, four general plans on which all 

 animals seem to have been modelled ; " viz. 



i. 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.. 



