Sponge and the Sponge Fisheries. 161 



southern part of the Sea of Okhotz, on the Asiatic conti- 

 nent, and specimens are not uncommon on the coasts of 

 Australia and New Zealand. In the Pacific they have been 

 found at the Kingmills Islands and Hawaiian Islands. 

 The extreme outlying form to the north, on both sides of 

 the Atlantic, is the excessively coarse Dysidea fragilis, with 

 its fibres loaded with debris. Those from the Cape of 

 Good Hope and Southern Australia also belong to the 

 coarser genera. The species cited by Miklucho Maclay 

 from the Sea of Okhotz seems to be one of the Phyllo- 

 spongidce, but there is no analysis of the characteristics of 

 the skeleton, only the external form being described and 

 figured in his article on the sponges of the North Pacific 

 (" Memoires de. 1'Acad. Imp. de St. Petersburg," vol. 75, 

 No. 3). It would seem, therefore, that the finer skeletons 

 of the Keratosa, those of the genus Spongia, are only to 

 be sought in the intermediate zone, where the waters are of 

 equable and high temperature. Again, in examining the 

 species of this genus with relation to each other, it becomes 

 equally evident that they are finest and most numerous in 

 archipelagoes, or off coasts which are bordered by large 

 numbers of islands, or long reefs, or in sheltered seas. 



Mr. Gurdon Saltonstall states that the sponges near 

 Nassau lie on reefs very much exposed to the action of 

 the waves, often 30 miles from land, and always in 

 currents, sometimes running three or four knots an hour. 

 Such currents are usual wherever groups of islands confine 

 the tide water within certain definite channels, and they 

 have also the effect of concentrating the floating food in 

 the channels, or wherever tides meet. Both of these con- 

 ditions are essential to successful sponge growth, namely, a 

 continuous renewal of aerated water and a plentiful supply 

 of food, and are probably partly the cause of their abun- 



M 



