94 A COURSE ON ZOOLOGY. 



etc., whatever their external differences of appearance 

 may be, have many points in common, and it cannot be 

 denied that all have descended from a single primitive 

 type. This type is not known to us, for there is no wild 

 dog, using the word in its true sense. There is, indeed, 

 in the Antilles a race of wild dogs living in an untamed 

 state, but they are descendants of dogs taken there by 

 Christopher Columbus and his followers, and have be- 

 come savage by the absence of civilization and masters. 

 It is worthy of note that wild dogs do not bark, neither 

 do the wolf and jackal, both species being closely allied 

 to the dogs ; they howl, and acquire the faculty of bark- 

 ing only after they have been domesticated. 



We cannot enter into details concerning the distinctive 

 characters of the races of dogs that have been mentioned, 

 saying only that the form of the head and the strength 

 and length of the limbs are the points in which differences 

 are most marked. In this chapter we have limited our- 

 selves to an anatomical study of the dog in general, this 

 animal serving as our type of quadruped. 



CHAPTER IX. 

 The Chicken. 



IF we first study the external characteristics of the 

 chicken, we notice the following peculiarities : 



The animal is covered with an epidermic growth called 

 feathers. 



It is biped, and supports itself on its posterior digits, 



