SCIENTIFIC ADVANTAGES OF AN ANTARCTIC EXPEDITION. 421 



The CottidiB are replaced by six genera of TrachinidiB, remarkably 

 similar in form to Arctic types. * * * Gadoid fishes reappear, but 

 are less developed; as usual^ they are accompanied hj Myxine. The 

 reappearance of so specialized a genus as Lycodes is most remarkable.'' ^ 



These statements with reference to shore fishes might, with some 

 modifications, be repeated concerning the distribution and character of 

 all classes of marine invertebrates in high northern and high southern 

 latitudes. The Challenger researches show that nearly 250 species 

 taken in high southern latitudes occur also in the ISTorthern Hemisphere, 

 but are not recorded from the tropical zone. Fifty-four species of sea- 

 weed have also been recorded as showing a similar distribution.^ Bipo- 

 larity 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, 

 Lamellibranchs, 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, Holothuroidea, 

 Annelida, Amphipoda, Isopoda, and Tunicata. This difference is in 

 direct relation with the temperature of the water in which these organ- 

 isms live, carbonate of lime being thrown dow7i much more rapidly and 

 abundantly in warm than in cold water by ammonium carbonate, one 

 of the waste products of organic activity. 



In the Southern and Subantarctic 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 

 the body of the parent, and have a kind of commensal 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 development between Arctic and Antarctic Echinoderms (and the 

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

 classes of Invertebrates, and probablj^ 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 can not be 

 doubted that an Antarctic expedition would bring back collections 

 and observations of the greatest interest to all naturalists and physi- 



'Giinther, Study of Fishes, pages 282-290. (Edinburgh, 1880.) 

 2 Murray and Barton. Phycological Memoirs of the British Museum, part 3. 

 (London, 1895.) 



