282 NATURAL SCIENCE. Oct.. 



atmospheric pressure becoming quite different. Even the temperature 

 alone cannot be compared, for near the surface it diminishes very 

 rapidly, and then more and more slowly until we reach the tempera- 

 ture of the abysses. ]\Ioreover, at a given time the temperature of a 

 certain depth may be the same as that of the surface in a higher 

 latitude, but the variations are quite different. In the Mediterranean 

 the daily variations cease totally at i8 m., the seasonal at about 400 m., 

 and as we have seen, the variations are much more important than 

 the average temperature. 



It was formerly concluded on theoretical grounds that there could 

 be as well many vertical belts of different life as there are horizontal 

 ones, but this comparison is, as I have shown, not correct or can only be 

 carried to certain depths, not exceeding 400 m. This is not a theo- 

 retical conclusion onl}^ All the unerring data, proving a relation 

 between the diminishing of temperature in horizontal and vertical 

 direction, are obtained in depths within the 200 m. limit.-^ 



Considering the above facts, I do not think the horizontal distribu- 

 tion of the pelagic fauna is compensated by the vertical differences, so 

 that pelagic animals would find the same temperature that they have 

 near the surface in higher latitudes in a low latitude in greater depth. 

 Vertical migrations cannot be so extensive (owing to the sniall power 

 of locomotion of the Plankton animals) ; and in the greater depths 

 conditions prevail which exist nowhere at the surface, in no latitude, 

 and in no time of the year. 



Somewhat striking are the observations of Chun, who found the 

 surface animals of the winter in the Mediterranean at considerable 

 depth in the summer. Setting aside the question as to whether his 

 apparatus was adequate to prove with certainty the depth from which 

 the animals are supposed to come, his observations can be explained 

 by the influence of temperature. 



In the Mediterranean the deep water is much warmer than in the 

 Atlantic ; the retreating animals would, therefore, not find such 

 extremes of temperature as in the open ocean (which is, as Agassiz 

 has stated, in some places, at least, totally destitute of pelagic life in 

 such depths). In the IMediterranean, therefore, an intermediate 

 pelagic fauna would be able to exist under the special life-conditions. 



This is in full harmony wdth the investigations of the Prince 

 of Monaco on the survival of the deep-sea animals of the Medi- 

 terranean. Formerly it was thought that the great atmospheric 

 pressure is the most important factor in deep-sea life, and it had been 

 concluded that the deep-sea animals coming to the surface would 

 be killed principally by the great diiTerence of the atmospheric 

 pressure ; but that has been refuted by the Prince. Atlantic animals 



^ Echinocanlium kurtzii 1 occur in the Florida stream in a depth of 25 m., in North 

 Moira atropos > Carolina at the surface. 



A ■ J. ■ J., (in the ]\Iediterranean near the surface, in the tropical 



Acgtnopsts mcditcrranca - . , . . 



I Atlantic in 200 m. 



