1899] LIFE HIGH AND LOW 165 



population when the nature of the bottom deposit changes. It has 

 been a laborious piece of work, executed with patient carefulness, and 

 the results though not startling are certainly valuable. 1 



Since the principal object of the investigation was to study the 

 relation of the fauna to the bottom-deposit, the area selected for 

 examination was so chosen that the general physical conditions were 

 uniform apart from the nature of the deposits, and the amount of 

 disturbance of the bottom water by the action of waves was relatively 

 small. The chief results to be gained by carefully scanning the 

 numerous tables — the drawing up of which must have meant a large 

 amount of work — relate to the suitability of certain kinds of ground 

 for certain kinds of animals, but apart from this the memoir is also 

 interesting because of the numerous notes on the habits of the animals 

 and for its analysis of the environmental conditions. 



The physical conditions, the variations of which influence the life 

 of bottom-living species, are capable of definite statement, and for the 

 most part of accurate measurement. They are — 



1. The constitution of the sea- water. 



2. The nature of the bottom-deposit. 



3. The movements of the water, due to 



(a) wave action, 



(b) currents, 



(c) tides. 



4. The temperature of the sea-water. 



5. The pressure, varying with the depth of water. 



6. The amount of light which penetrates to the bottom. 



The external biological conditions influencing the distribution of 

 any bottom-loving organism, due to the existence at the same time ot 

 other living organisms, are often of a complicated nature. 



1. One organism may exert an advantageous influence upon another.. 



(a) By serving as its food-supply ; 



(b) By serving as a fixed base to which it may attach itself ; 



(c) By serving as a movable base, and thus extending the 



area over which a fixed organism can collect its food- 

 supply ; 



(d) By bringing supplies of food to the other organism as 



well as to itself, either by setting up a current, or in 

 some other way ; 



(e) By affording the other organism means of protection or 



concealment from its enemies. 



2. One organism may exert a disadvantageous influence upon 



another. 

 (a) By preying upon it ; 



1 " On the Fauna and Bottom-deposits near the Thirty-fathom Line from the Eddystone 

 Grounds to Start Point," Journ. Marine Biol. Ass. v. June 1899, pp. 365-542, 15 charts 

 and 7 tables. 



