662 DEPTHS OF THE OCEAN 



Another series of investigations in this field were those 

 of C. G. J. Petersen, regarding the distribution of mollusca in 

 the Kattegat. In The Cruises of the '' Haitch,'' Petersen^ has 

 employed the only empirical method of investigating the 

 distribution of animals, viz. to analyse the distribution of species 

 in relation to various external conditions, as for instance, high 

 or low salinity, high or low temperature, great changes in 

 temperature or salinity, etc. It proved possible in the Kattegat 

 to define areas of distribution of certain species, coinciding with 

 areas where characteristic physical conditions prevailed. 



Similar methods have been employed by Chun for the study 

 of pelagic organisms. An important branch of this science has 

 the object of studying the changes occurring in the physical 

 conditions of the ocean, and the influence of these changes on 

 the occurrence or abundance of organisms. By means of a 

 continually increasing co-operation between hydrography and 

 biology, both equally necessary in the study of such problems, 

 oceanography has made great progress, especially during the 

 international investigations in the study of the sea. 



The additions which during the cruises of the " Michael 

 Sars " it has been possible to make to these branches of science 

 consist mainly of information regarding the vertical and 

 horizontal distribution of animals, accompanied by physical 

 observations of various kinds. These, biological and physical 

 investigations place us in a position to test certain ideas regard- 

 ing the adaptations of animals, and thus acquire knowledge on 

 certain important mechanisms of life. 



The following review of some of our principal results can 

 by no means claim to be complete. The literature referred to, 

 the various fields of biology discussed, and even the selection 

 made from the material collected by our recent expedition, have 

 all been limited for the purpose of this review. Still I hope to 

 indicate some new contributions to science, and at the same 

 time to convey some idea of the general methods and aims of 

 biological oceanic research. 



Colours of Marine Animals 



From time immejnorial seafaring men have possessed a 

 certain amount of knowledge as to the colours of marine animals. 



of 1882 (H.M.S. 'Triton')," Proc. Roy. Soc. Loud., vol. xxxv. p. 202, 1883; Murray, "The 

 physical and biological conditions of the seas and estuaries about North Britain," Froc. Phil. 

 Soc. Glasgow, vol. xvii. p. 306, 1886. 



1 Petersen, Det videtiskabelige Udbytte af Kanonbaaden '' Haiuhs" togier, Kjobenhavn, 1893. 



