INTRODUCTION. 



OBJECT AXD Th\y OF THE WORK MAPS EXPLAINED — SUBSIBENCE ELEVATION — TERTTARY 



FORJIATIONS — GLACIAL ACTION SARGASSO SEAS DISTRIBUTION. 



The great amount of infonnation which has of late years been accumulated regarding the Geo- 

 graphical Distribution of Plants and Animals renders it very desirable that it shoidd be 

 classified and displayed, so that some general and connected view of the facts, and of their bearing 

 on each other, may be obtained. To do this is the object of the present work. 



I shall to a certain extent follow the arrangement suggested by Schouw,* and adopted by 

 Decandollet and others in regard to plants, and consider the subject under two aspects equivalent 

 to those which in Zoology Van Der HoevenJ has recently proposed to distinguish respectively by 

 the names of " Geographical Zoology " and " Zoological Geography," the former referring to the 

 range of species, the latter to the Faunas of districts, and treat each great class separately and 

 independently upon both these points. 



I shall commence with the former, and shall first pass the different families in each class under 

 review, giving an account of their distribution, and afiinities. 



Their history and that of their nearest relatives during past geological epochs is a most impor- 

 tant point in relation to this, and to these I propose to give special attention ; and I shall endeavour, 

 by the aid of maps, to exhibit the facts more clearly and comprehensively than I could otherwise do. 

 On these maps the localities where the groups or species are found will be marked ; and the districts 

 where they are most fully or most feebly represented wQl, when necessary, be shown by different m- 

 tcnsitics of colour. To save expense, and so to allow of greater use being made of maps than would 

 otherwise be the case, they have been drawn of three sizes, so that, when a mere general reference 

 is reqiured the smaller ones may be used, and the larger be reserved for those cases which 

 require more detail. Where the distribution of a species or group is peculiar, any speculations 

 which have been made as to its cause will be noticed. 



After a full inquiry into the Geographical Zoology of each class, I shall conclude its history 

 with a summary of its Zoological Geography. The geographical distribution of each class will 

 thus form an independent treatise by itself. 



While the work is mainly addressed to the scientific naturalist, it is also intended for the 

 general reader ; and with this view, scientific names will be avoided whenever there are 



* ScHOUw, "GrundzeugeeinerallgemeinenPflanzengcograpliie." Berlin, 1823, p. 4. 



t Decandolle, "Geographie Botanique." Paris and Geneva, 1855. 



t J. Van Der Hoeven, " Philosophia Zoologica." Leydeu, 1864, p. 375. 



