INTRODUCTION. 



In the preceding part of our work, we have discussed the 

 geographical distribution of animals from the point of view of 

 the geographer; taking the different regions of the earth in 

 succession, and giving as full an account as our space would 

 permit of their chief forms of animal life. Now, we proceed 

 from the standpoint of the systematic zoologist ; taking in 

 succession each of the families with which we deal, and giving 

 an account of the distribution, both of the entire family and, as 

 far as practicable, of each of tlie genera of whicli it is composed. 

 As in the former part, our mode of treatment led us to speculate 

 on the past changes of the earth's surface ; so here we shall 

 endeavour to elucidate the past migrations of animals, and thus, 

 to some extent, account for their actual distribution. 



The tabular headings, showing the range of the family in each 

 region, will enable the reader to determine at a glance the 

 general distribution of the group, as soon as he has familiarised 

 himself, by a study of our general and regional maps, with the 

 limits of the regions and sub-regions, and the figures (1 to 4) 

 by which the latter are indicated. Much pains have been taken, 

 to give the number of the known genera and species in each 

 family, correctly ; but these numbers must, in most cases, only 

 be looked upon as ajDproximations ; because, owing to constant 

 accessions of fresh material on the one hand, and the discovery 

 that many supposed species are only varieties, on the other, such 

 statistics are in a continual state of fluctuation. In the number 

 of genera there is the greatest uncertainty ; as will be seen by 

 the two sets of numbers sometimes given, which denote the 

 genera according to different modern authorities. 



