THE ANIMAL KINGDOM. 



SUB-KINGDOM I,— VERTEBRATA. 

 CLASS I.— MAMMALIA. 



By R. Lydekker, B A . FES, V P G.S , &c. 



It is a somewhat curious deficiency in the Eng;lish language that it has no 

 word of its own that will include all the animals forming the class known to 

 zoologists as the Mammalia. It is true that the term Beasts properly belongs 

 to the great majority of the members of the class, but it has also acquired 

 another meaning, and expressly excludes man. Even more objectionable is 

 the term Quadrupeds, since not only does this exclude man and the higher 

 apes, but etymologically includes crocodiles, lizards, and turtles. Accord- 

 ingly, as neither of these two words are suitable to designate the class as a 

 whole, naturalists have long been in the habit of using an Anglicised version 

 of its scientific designation, and at the present day the term " Mammals " has 

 come so widely into use that no apology for its employment here is called for. 

 Mammals, then, are 1 ho highest of the Vertebrata, and thus of all animals, and 

 take their name from the general presence of prominent udders, furnished 

 with teats, in the female, for the secretion of the milk, by which the young are 

 invariably fed during the earlier stages of their existence, such udders being 

 situated in the higher types on the breast, although in many of the lower 

 forms they are abdominal in position. In the very lowest members of the class 

 there are, however, no distinct teats, the milk-glands discharging by means 

 of a number of small apertures in the skin of the lower surface of the body. 

 It is thus the presence of these milk -glands, and the suckling of the more or 

 less helpless young, that are the prime essential features of the class. 



Before glancing at certain others of their distinctive features, a few words 

 may be said in regard to the Vertebrata, wliich form a sub-kingdom, including 

 the five classes of Mammals (Mammalia), Birds (Aves), Rep- f.]j,i.acteristics 

 tiles (Reptilia), Amphibians (Amphibia), and Fishes (Pisces). ^^ vertebrates 

 And here it may be noticed that certain low forms, such as 

 the lampreys and lancelet {Amphioxus), commonly classed among Fishes, are 

 now regarded as forming a portion of a lower group known as the Protochor- 

 data. Vertebrates take their name from the general presence of the struc- 

 ture termed the vertebral column, or backbone, although in some of the lower 

 forms this is represented merely by a cartilaginous rod. Whether this struc- 

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