614 ZOOLOGY SECT. 



The general relations of the zoo-geographical regions may be 

 expressed in a diagrammatic form as follows : - 



PALAEARCTIC N E A R C T I C 



ORIENTAL POLYNESIAN 



ETHIOPIAN AUSTRALIAN NEW ZEALAND NEOTROPICAL 



I'IG. 1253. Diagram showing the general relations of the zoo -geographical regions. 



2. BATHYMETRICAL DISTRIBUTION. 



The foregoing pages have given a brief sketch of the facts 

 connected 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 possess 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, Echinodermata, Turbellaria, 

 Nemertinea, Polychaeta, Polyzoa, Brachiopoda, decapod Crustacea, 

 Pelecypoda, Gastropoda, Octopoda, and Teleostei. Numerous 

 examples of other groups Protozoa, the lower Crustacea, Insecta, 

 and Elasmobranchii are also littoral, and Penguins, Seals, and 

 Sirenia may be included in the list. 



Next in abundance to the littoral is the pelagic or ocean- 

 surface fauna, including animals which live haoitually on the 

 surface or at slight depths of the ocean, often far from land. 

 Amongst them are many Foraminifera, such as Globigerina and 

 Hastigerina, the Radiolaria, the Siphonophora, the majority of 

 Medusae, both hydrozoan and scyphozoan, nearly the whole class 

 of Ctenophora, many Entomostraca and Schizopoda, the hemi- 

 pterous Insect Halobates, the Pteropoda, Heteropoda, and some 

 other Gastropods, such as Glaucus, most Cephalopods, Pyrosoma 

 and the Salps, numerous Teleosts, such as Herrings, Flying-fish, 

 Mackerel, &c., the greater number of Sharks, and the majority of 

 Cetacea, 



