210 Fortieth Annual Meeting 



portant determining factor in the food supply of the larger 

 marine animals. 



(c) The benthos is the term applied to the third class of 

 organisms in the ecology of the ocean, namely, the dwellers 

 upon the sea bottom. The conditions of deep sea life in- 

 volve various factors not operating at the surface, such 

 ns enormous pressure, lack of sunlight, etc., and these pro- 

 foundly affect the structure and activities of the deeper ben- 

 thal fauna. The most fundamental ecological factor, in 

 this association, however, is the actual sea bottom itself. 

 This element confines the life-activities of many of its in- 

 habitants more completely within the horizontal plane than 

 do the influences limiting plankton, the individuals of which 

 move freely in three dimensions between the ocean surface 

 and sea-floor. With this difference in habit is correlated 

 the animal form. While the plankton tend to be either 

 spherical, disk-like, or top-shaped, that is, of a form adapted 

 rather for flotation than for progression in a definite direc- 

 tion (e.g. radiolaria, medusae, scyphomedusie, siphono- 

 phores), among the benthal animals, on the contrary, only 

 those typically attached, or derived ancestrally from at- 

 tached forms, exhibit radial symmetry, while the creeping 

 habit of the independent bottom forms as well as the sec- 

 ondarily acquired swimming habits of the nekton, are 

 correlated with the development of bilaterality and ceph- 

 alization. 



Many of the deep-sea animals, especially those which, 

 like the bottom fishes, have a body cavity into which the 

 water does not penetrate, are constituted so as to with- 

 stand enormous pressure at great depths. Another pecu- 

 liarity of the 1)enthos is the extent to which phosphorescence 

 runs rioi, and there seems good ground to believe that, in- 

 stead of intense darkness, the sea-bottom is bathed with 

 a phosphorescent glow, which in a measure takes the place 

 of sunlight, and gives sufficient illumination for animals 

 possessing eyes to see their way about. 



With reference to the all-important food relation, the 



