364 



SCIENCE. 



[N. S. Vol. III. No. 62. 



tion. Every attemiJt to treat iiuiformly ani- 

 mal groups, differing in this respect, or even 

 the attempt to compare them, is destined to be 

 a failure. 



The fourth chapter treats about the marine 

 zoogeographical regions. Ortmann constructs 

 these regions according to the most important 

 physical conditions which are of value to the 

 geographical distribution of animals. It is ne- 

 cessary to examine the relations of each group 

 of animals and each species of the general laws 

 of distribution, and it is, therefore, the aim of 

 scientific zoogeography to solve the question how 

 the single animals behave towards the general 

 laws. From this it follows that for the deter- 

 mination of general regions of distribution we 

 have to consider separately each life region, since 

 the fundamental physical conditions are totally 

 different in every one of them. 



The physical regions of the litoral life zone. 

 The principal characters of the litoral are: 1, 

 presence of light; 2, presence of the bottom; and 

 3, the presence of the medium, i. e. , the sea- 

 water. The litoral follows generally the coasts 

 of the continents, and extends only over that 

 part of the sea which borders the coast. The 

 distance is of course determined by the inclina- 

 tion of the sea bottom. The limit is the depth 

 to which daylight is able to penetrate, that is 

 about 400 m. Besides there are litoral regions 

 around each island or group of islands. The 

 close relation of the litoral to the land produces, 

 of course, a great difference in the facies, and, 

 therefore, we have very different conditions of 

 existence. The most important conditions are 

 the climatic differences. The litoral is divided 

 by Ortmann into the following regions: 



1. Arctic Region. 



a. Arctic circumpolar subregion. 



b. Atlantic boreal subregion (with two 

 local faunas). 



c. Pacific boreal subregion (possibly also 

 with local faunas). 



2. Indo-Pacific Region (very uniform). 



3. West American Region (very uniform). 



4. East American Region (probably with local 

 faunas). 



5. West African Region. 



a. Mediterranean subregion. 



b. Guinea subregion. 



6. Antarctic region (numerous local faunas). 



The abyssal life regions. 



The principal characters of the abyssal con- 

 sist in the complete absence of sun light, uni- 

 form cold temperature, relative state of rest of 

 the medium and the slightly differentiated char- 

 acter of the facies. In its low temperature the 

 abyssal approaches the Arctic literal. The 

 extension of the abyssal is enormous ; it covers 

 the whole bottom of the oceans. Topographi- 

 cally the abyssal of the whole earth is continu- 

 ously connected. Therefore, it is impossible, so 

 far, to divide the abyssal into different regions. 



The physical regions of the pelagic life zone. 



The pelagial resembles the litoral in the pres- 

 ence of sun light, but differs from it in the 

 absence of the 'bottom.' In regard to tem- 

 perature it is also more like the litoral. There 

 is more variety than in the abyssal. The hori- 

 zontal extension of the pelagial agrees nearly 

 completely with the abyssal, and is therefore 

 topographically uninterrupted. 



But here the climatic conditions act in a man- 

 ner similar to those of the litoral. In the 

 equatorial regions we find the surface of the 

 water of equally high temperature. Towards 

 the poles the temperature becomes lower, and 

 the amplitude of the oscillations increases; still 

 farther towards the poles, the temperature of 

 the water becomes again more uniform but 

 cold. 



The Pelagial is divided by Ortmann into four 

 regions : 



1. Arctic Region. 



a. Arctic-circumpolar subregion. 



b. Atlantic-boreal subregion. 



c. Pacific-boreal subregion. 



2. Indo-Pacific Region. 



3. Atlantic Region. 



4. Antarctic Region. 



a. Notal *-circumpolar subregion. 



* Ortmann was unable to trace the name noialian, 

 ■whose original appliance by Gill was introduced in 

 1884 in a very interesting paper. The Principles of 

 Zoogeography, a presidential address delivered at the 

 third anniversary meeting ol: the Biological Society 

 of Washington, January 19, 1883. Proc. Biol. Soc. 

 Washington, Vol. II., 1882-1884, pp. 39. Washing- 

 ton, 1884. 



