I04 OUTLINES OF NATURAL HISTORY. 



and circular pupil of tlie eye. According to Cuvier, the 

 Dog is " the most complete and most useful conquest that 

 man has made. The whole species has become our pro- 

 perty ; each individual is entirely devoted to his master, 

 adopts his manners, distinguishes and defends his property, 

 and remains attached to him even unto death ; and all 

 this springs not from mere necessity, nor from constraint, 

 but simply from gratitude and true friendship. The 

 smftness, the strength, and the highly developed power of 

 smelling of the dog, have made him a powerful ally of 

 man against the other animals, and were perhaps neces- 

 sary to the establishment of society. It is the only ani- 

 mal that has followed man all over the earth." 



Recapitulation of Essential Characters. — The 

 animal is an air-breather, and at no time of its life possesses 

 gills. The breathing-organs are in the form of lungs, 

 which do not communicate with air-receptacles or with 

 the interior of the bones. The blood is hot, and the 

 heart four-chambered. The skull is united to the back- 

 bone by a double joint, and the lower jaw is joined to the 

 skull directly, and not by means of a " quadrate bone." 

 The skin is provided with the peculiar appendages which 

 are known as hairs. The animal brings forth its young 

 alive, and the young are nourished for a longer or shorter 

 time by the mother by means of a special secretion — the 

 milk — secreted by means of special glands — the mammary 

 glands. 



CHAPTER XXIV. 



THE SUB-KINGDOMS, 



It remains very briefly to consider how the classes of 

 which we have examined rep"resentative types, can be 

 arranged into larger divisions. The possibility of such 

 an arrangement depends upon the fact that certain classes 



