xxiv SCIENCE PROGRESS. 



limits of range, on means of dispersal, and that the two latter influences are different for 

 different animals. 



Dr. Ortmann considers that the pecularities in the conditions of existence which affect 

 animal life may conveniently be grouped under three headings, as those which have to do with 

 light, medium and substratum. Without light there is no vegetation. Without vegetation 

 there is no food which animals can assimilate. According to the medium in which they live 

 they must be fitted for air-breathing or water-breathing. The substratum may be dry land or 

 ocean floor, but those animals which are dependent upon either must have the locomotive 

 apparatus by which they obtain their food adapted accordingly. From these considerations 

 Dr. Ortmann divides the globe into five principal life-areas. The medium distinguishes the 

 land-area, of which the occupants are air-breathers, from all the rest. The abyssal area is set 

 apart from all by the absence of light. The pelagic area stands alone in having occupants 

 independent of any solid resting-place. The fluvial or fresh water area carries its characteristic 

 in its name, and there remains the littoral area, not so sharply marked off as the others, but 

 perhaps the most important of all, if from its teeming bosom the thronging forms of life have 

 felt and found thei.r way into all the other areas, spreading over the high seas, colonising the 

 profoundest abysses, threading their course up estuaries and rivers, climbing the terraces of 

 the land and taking wing beyond the clouds. 



By paying regard to climatic and topographical relations, Dr. Ortmann finds himself able 

 to subdivide the littoral and the pelagic areas into regions and subregions. In each there is 

 an Arctic, an Antarctic, and an Indo-pacific region. In the pelagic area there is also an 

 Atlantic region, while in the littoral there are three additional regions, a West-American, an 

 East-American, and a West-African. In the last a Mediterranean subregion is distinguished 

 from a Guinea subregion, and there are similar and further subdivisions suggested in some of 

 the other areas. Only the abyssal area is spoken of as "without differentiation into regions 

 and subregions ". As distinguished from the Continental, Freshwater, and Littoral areas, the 

 author maintains that " in the Abyssal and Pelagic areas the continuity is complete, in no part 

 of the earth are special portions of these two topographically separated from others, but every- 

 where they stand in direct communication ". This mode of viewing the abyssal area seems to 

 be of very doubtful validity. There are submarine mountains, submarine lakes, warm currents 

 and cold currents functioning as submarine rivers, which must operate as climatic and topo- 

 graphical barriers as forcibly in the unlighted marine abysses as they do in the realms of day- 

 light. Considering, too, the intimate dependence of animal life upon the available food, it 

 would be strange indeed if no regions and subregions were marked by the varying character 

 of the ocean floor, with its diatom ooze and radiolarian ooze and globigerina ooze, and other 

 distinctive coatings. Were the deep sea in fact an uninterrupted uniform expanse, it might be 

 expected, and at one time was expected, to have a fauna common to the whole of it. But of 

 this there is at least no striking evidence, and Dr. John Murray of The Challettgc}- adduces 

 some evidence which is rather striking in the contrary direction. Thus at a station in mid- 

 equatorial Atlantic, in 1850 fathoms, 38 species were obtained. At a station in mid-equatorial 

 Pacific, in 2425 fathoms, 29 species were obtained. Both were on globigerina ooze. Only one 

 species was common to the two localities, and that one the little Disciua Atlantica, belonging 

 to a genus which ranges from the Cambrian to the present time. 



In the vast area of the subject there are many regions and subregions of discussion into 

 which this short notice cannot follow Dr. Ortmann. All that he has to say, whether it com- 

 mands assent or otherwise, will be found worthy of attention. He brings very clearly into view 

 the merits and occasionally the demerits of his predecessors. He shows how much we have 

 still to learn, what points of vantage have been attained, in what direction the line of advance 

 should be followed with most hope of success. The zoologist can scarcely peruse this memoir 

 without finding that his own scientific studies from one side or another are closely connected 

 with the complex problem of the distribution of animals. 



