president's address. 15 



accounted for, according to Sir John Murray and others, by the rate 

 of metaboUsm in the organisms. The assemblages captured in cold 

 polar waters are of different ages and stages, young and adults of 

 several generations occurring together in profusion,' and it is supposed 

 that the adults ' may be ten, twenty or more years of age.' At the 

 low temperature the action of putrefactive bacteria and of enzymes 

 is very slow or in abeyance, and the vital actions of the Crustacea 

 take place more slowly and the individual lives are longer. On the 

 other hand, in the warmer waters of the tropics the action of the 

 bacteria is more rapid, metabolism in general is more active, and the 

 various stages in the life-history are passed through more rapidly, 

 so that the smaller organisms of equatorial seas probably only live for 

 days or weeks in place of years. 



This explanation may account also for the much greater quantity 

 of living organisms which has been found so often on the sea floor 

 in polar waters. It is a curious fact that the development of the 

 polar marine animals is in general ' direct ' without lai-val pelagic stages, 

 the result being that the young settle down on the floor of the ocean 

 in the neighbourhood of the parent forms, so that there come to be 

 enormous congregations of the same kind of animal within a limited 

 area, and the dredge will in a particular haul come up filled with 

 hundreds, it may be, of an Echinoderm, a Sponge, a Crustacean, a 

 Brachiopod, or an Ascidian; whereas in warmer seas the young pass 

 through a pelagic stage and so become more widely distributed over 

 the floor of the ocean. The Challenger Expedition found in the 

 Antarctic . certain Echinoderms, for example, which had young in 

 various stages of development attached to some part of the body of the 

 parents, whereas in temperate or tropical regions the same class of 

 animals set free their eggs and the development proceeds in the open 

 water quite independently of, and it may be far distant from, the 

 parent. 



Another characteristic result of the difference in temperature is that 

 the secretion of carbonate of lime in the form of shells and skeletons 

 proceeds more rapidly in warm than in cold water. The massive shells 

 of molluscs, the vast deposits of carbonate of lime formed by corals 

 and by calcareous seaweeds, are characteristic of the tropics; whereas 

 in polar seas, while the animals may be large, they are for the most 

 part soft-bodied and destitute of calcareous secretions. The calcareous 

 pelagic Foraminifera are characteristic of tropical and sub-tropical 

 plankton, and few, if any, are found in polar waters. Globigerina 



' Whether, however, the low temperature may not also retard reproduction 

 is worthy of consideration. 



