634 ZOOLOGY sect. 



The negative characteristics of this region are also very remarks 

 able. Except in Central America and the West Indies, there are 

 no Insectivora ; Civets, Oxen, Sheep, Antelopes, and true Swine 

 (Sidncc) are altogether absent, and there are very few species of 

 Deer; Crows and Eavens are also practically unrepresented. 



In the West Indies there are no Edentata, Monkeys, or Car- 

 nivora, and there occurs a peculiar Insectivore, SoUnodon, belong- 

 ing to the Centetida3, otherwise found only in Madagascar. The 

 Galapagos Archipelago, a group of oceanic islands, about 600 miles 

 to the west of the continent, have at the most two Mammals, a 

 Bat and a Mouse ; their Birds are very different from those of the 

 mainland, and include many endemic species; and among the 

 E,eptiles are the gigantic Tortoises (Testudo), of which different 

 species occur in the various islands. 



The general relations of the zoo-geographical regions may be 

 expressed in a diagrammatic form as follows : — 



PALAEARCTI C N E A R C T I C 



ORIENTAL POLVNESIAN- 



ETHIOPIAN AUSTRALIAN — NEW ZEALAND NEOTROPICAL 



Fig. 1241. — DLagrani showing the general relations of the zoo-geographical regions. 



2. Bathymetrical Distkibution. 



The foregoing pages have given a brief sketch of the facts con- 

 nected with geographical or horizontal distribution. We now turn 

 to bathymetrical or vertical distribution — the facts concerning the 

 distribution of animals at various depths of the sea or of lakes, and 

 at various heights of the land. 



The region of greatest abundance of marine life, as regards 

 both the number of genera and species and of individuals, is the 

 littoral or shore-region. The rocks left dry by the retreating 

 tide, the rock-pools exposed at low water, and the forests of kelp 

 at the limit of low tide or a few fathoms below, possesses an extra- 

 ordinarily rich and abundant fauna, including all the Calcareous 

 Sponges and a large proportion of the remaining groups, Hydroid 

 Zoophytes, Sea-anemones and Corals, Echinoderms, Turbellaria, 

 IS'ermertinea, Polychoeta, Polyzoa, Brachiopods, decapod Crustacea, 

 Pelecypods, Gastropods, Octopods, and Teleostei. Numerous 

 examples of other groups — Protozoa, the lower Crustacea, Insects, 



