THE HAUNTS OF LIFE 91 



be little doubt that these elongated limbs are suitable for 

 moving delicately on the soft surface. Some of the Deep- 

 Sea Brittle-stars show a great reduction of the central disc 

 and a great elongation of the arms as compared with shallow 

 water forms. It may be noted that the extraordinary 

 elongation of hmbs and the Hke is quite incompatible with 

 any conditions except those of perfect cahn. 



Many Deep-Sea animals are very delicately built, with 

 bodies thoroughly permeable by water. A deUcate struc- 

 ture like Venus's Flower Basket (Euplectella) which is 

 shivered in a child's fingers, is admirably suited to great 

 depths where there are tons of pressure on the square inch. 

 The whole body is open to the water and the pressure is not 

 felt. For while a hermetically sealed glass vessel is crushed 

 in when it is lowered into deep water, an open glass vessel, 

 no matter how delicate, is not afiected. On the Challenger 

 expedition, Mr. J. Y. Buchanan made an instructive experi- 

 ment which has been often cited. He took a hermetically- 

 sealed empty glass cylinder, wrapped it up in flannel, en- 

 closed it in a copper cylinder with perforated ends, and 

 lowered it to 2,000 fathoms. At a certain depth the glass 

 cylinder was shivered into snowy powder, for its walls could 

 not withstand the increasing outside pressure of the water. 

 The shivering took place so suddenly that before water 

 could rush in to fill the vacant space, one side of the 

 copper cylinder caved in. As Prof. Wyville Thomson said, 

 an ' implosion ', not an explosion, occurred. 



When an abyssal fish rising suddenly gets into a zone of 

 much reduced pressure, the gas in its swim-bladder, which 

 had its pressure adjusted to the greater depth, expands, 

 and the fish, in spite of itself, is hurried to the surface, 

 ' tumbling upwards', as Professor Hickson puts it. The 



