ROMANCE OF DEPTHS OF THE SEA 109 



may be connected with the temperature at which 

 they live that they show a marked inability to 

 secrete calcareous skeletons : the bones of deep- 

 sea fishes are curiously soft and their scales thin. 

 Their bodies, or muscles, have lost the usual 

 elasticity, and when one pinches a hake, as when 

 one pinches a patient suffering from beri-beri, 

 the mark of the finger and thumb persists. Even 

 the deep-sea sea-urchins present but a soft skele- 

 ton, and the carapace of the Crustacea becomes 

 chitinous, even the shells of the mollusca thin 

 and translucent. Calcareous sponges have not 

 been found in the depths. The exact reason for 

 this deficiency in the power of depositing lime is 

 obscure. It is certainly not due to a lack of 

 material dissolved in the surrounding waters ; 

 but it is curious to remark that animals with a 

 flinty skeleton seem to show an increased power 

 of secreting silica in deep-sea waters. Another 

 unexplained peculiarity of deep-sea animals is 

 their tendency to reduce the size of their breathing 

 apparatus. The gills are reduced in number and 

 in size, and in some cases have almost disappeared. 

 There is also a great tendency amongst deep-sea 

 organisms to produce spines and processes a fact 

 which is recorded over and over again in the 



