
912 THE AMERICAN NATURALIST. [VoL. XXXVI. 
In the brief introduction (pp. 1-4) the class Mammalia is very 
satisfactorily defined; and in reference to their position as the 
“highest of the Vertebrates,” the term “highest,” in comparison 
with “ specialization," is considered, and its use in such a connection 
is amply defended, since “ specialization " does not necessarily imply 
the perfection and complexity of structure that is involved in the 
term “highest.” “Most specialized" and “highest,” and “least 
specialized” and “lowest” are therefore not the equivalent alter- 
natives some writers have considered them to be, and in preferring the 
former to the latter as more definite and exact expressions they have 
not thereby secured greater accuracy of statement. 
An exposition of the structure of mammals occupies pages 5-78, 
and deals concisely with their external form, skeleton, skull, teeth, 
the organs of digestion, respiration, reproduction, the brain, etc., 
with numerous well-chosen illustrations. The present distribution of 
the class and the subject of zoólogical regions is treated less satis- 
factorily (pp. 78-89): because the tiger “is as much at home in a 
tropical jungle as on the icy plains of northern Asia" is no proof 
that *the world cannot be mapped out into areas bounded by 
parallels of temperature "; because there are a few wide-ranging 
types it does not follow that temperature does not constitute one of 
the most powerful controlling influences in the distribution of life 
over the globe. The primary regions and their subdivisions here 
adopted are, however, those now most generally accepted. 
Chapter III (pp. 90-95) considers * The Possible Forerunners of 
the Mammalia,” and Chapter IV (pp. 96-104) is entitled “The 
Dawn of Mammalian Life "; both subjects are carefully and conserva- 
tively treated. The rest of the volume takes up the orders of 
mammals in their systematic sequence, from monotremes to primates. 
Respecting this part of the work the author says: *I have given, I 
hope, adequate treatment from the standpoint of a necessarily 
limited treatise to the majority of the more important genera of mam- 
mals both living and extinct." Such groups as the Edentata and 
Marsupialia are given relatively, and very appropriately, much more 
space than is accorded to many of the other orders. On the other 
hand, the Rodentia and Chiroptera, with their multitude of forms, are 
treated so briefly that one almost regrets that the plan of the work 
did not permit of an additional hundred pages or so, in order to 
more fully notice these and a few other groups now very briefly 
noticed or quite omitted. But the author has given us so much that 
is good in this excellent manual that it is rather ungracious to make 

