The Scientific Advantages of an Antarctic Expedition. 433 



250 species taken in high southern latitudes occur also in the 

 northern hemisphere, but are not recorded from the tropical zone. 

 Fifty-four species of sea-weed shave also been recorded as showing 

 a similar distribution.* Bipolarity in the distribution of marine 

 organisms is a fact, however much naturalists may differ as to its 

 extent and the way in which it has originated. 



All those animals which secrete large quantities of carbonate of 

 lime greatly predominate in the tropics, such as Corals, Decapod 

 Crustacea, Lameilibranchs, and Gasteropods. On the other hand, 

 those animals in which there is a feeble development of carbonate of 

 lime structures predominate in cold polar waters, such as Hydroida, 

 Holothurioidea, Annelida, Amphipoda, Isopoda, and Tunicata. This 

 difference is in direct relation with the temperature of the water in 

 which these organisms live, a much more rapid and abundant pre- 

 cipitate of carbonate of lime being thrown down in warm than in 

 cold water by ammonium carbonate, one of the waste products of 

 organic activity. 



In the Southern and Sub-antarctic Ocean a large proportion of the 

 Echinoderms develop their young after a fashion which precludes 

 the possibility of a pelagic larval stage. The young are reared 

 within or upon ihe body of the parent, and have a kind of com- 

 mensal connection with her till they are large enough to take 

 care of themselves. A similar method of direct development has 

 been observed in eight or nine species of Echinoderms from the 

 cold waters of the northern hemisphere. On the other hand, in 

 temperate and tropical regions the development of a free- swimming 

 larva is so entirely the rule that it is usually described as the normal 

 habit of the Echinodermata. This similarity in the mode of develop- 

 ment between Arctic and Antarctic Echinoderms (and the contrast 

 to what takes place in the tropics) holds good also in other classes 

 of Invertebrates, and probably accounts for the absence of free- 

 swimming larvae, of benthonic animals in the surface gatherings in 

 Arctic and Antarctic waters. 



What is urgently required with reference to the biological 

 problems here indicated is a fuller knowledge of the facts, and it 

 cannot be doubted that an Antarctic expedition would bring back 

 collections and observations of the greatest interest to all naturalists 

 and physiologists, and without such information it is impossible to 

 discuss with success the present distribution of organisms over the 

 surface of the globe, or to form a true conception of the antecedent 

 conditions by which that distribution has been brought about. 



new species being made from purely geographical considerations, see 'Summary of 

 Eesults, "Challenger" Expedition,' p. 1440-45. 



* Murray and Barton, ' Phycological Memoirs of the British Museum/ part iii. 

 London. 1895. 



