sponge and the Sponge Fisheries. 163 



to five fathoms. This fact also explains, in a measure, but 

 not wholly, the greater coarseness of American sponges as 

 compared with the European ; for though it may be 

 assumed from the examination of the skeletons that Medi- 

 terranean sponges are much less exposed to turbid waters, 

 and though it may be shown by the microscope that the 

 primary fibres contain less debris^ this does not wholly 

 explain their greater fineness and elasticity. We may 

 attribute this either wholly or partly to climatic con- 

 ditions. 



If either the temperature or density of the water had 

 been exceptional, we might have gained some additional 

 information, but as it is, we cannot assume that either 

 cause would have been sufficient to account for the absence 

 of the SpongicE from the Euxine. According to Carpenter, 

 in his articles on the Mediterranean and Black Sea, there 

 is a strong current continually flowing at the depth of 20 

 fathoms from the Mediterranean into the Black Sea, and a 

 return surface current from the Black Sea into the Mediter- 

 ranean. The sponges occur necessarily in the shallower 

 waters of the Sea of Marmora, since they are said by Von 

 Eckhel to be fished for mostly with the harpoon, and are 

 probably exposed more or less to the influence of the sur- 

 face current. Under these circumstances, they must very 

 often be able to endure a degree of cold during the winter, 

 and an amount of change in the density of the water, for 

 which it becomes difficult to account, even taking into con- 

 sideration the inferior quality of their skeletons. It is 

 possible, however, that the water of the northern part of 

 the Black Sea may not aff"ect the temperature of the 

 southern part to such an extent as would at first sight 

 appear probable, and that, notwithstanding the lower tem- 

 perature of the northern shores, the general temperature of 



