2 THREE CRUISES OF THE ' BLAKE. 



having been thus drawn up from a depth of two or three 

 miles, they should be in a very dilapidated condition. A num- 

 ber of the abyssal types among the fishes, mollusks, Crustacea, 

 echinoderms, and even rhizopods, are characterized by the loose- 

 ness of their tissues, which allows the water to permeate every 

 interstice, and to equalize the enormous pressure under which 

 they live. When this pressure is removed, the fishes, with their 

 flabby muscles, tender skins, and semi-cartilaginous skeletons, 

 literally fall to pieces t ; they suffer from the decomposition and 

 the dilatation of the air of the swimming bladder ; the eyes 

 are forced out of their sockets, and the scales fall off from 

 the delicate skin. The mollusks present shapeless masses diffi- 

 cult of study. The Crustacea seem to have been boiled, and 

 their soft and thin shells resemble those of their shallow-water 

 congeners just after moulting ; many of the annelids and echi- 

 noderms look as if they had been digested by some of the 

 larger deep-sea denizens, while the fragile types have lost their 

 delicate appendages, or have become crushed in the ascent. 

 Yet we know that a number of species of all these classes can 

 thrive under differences of pressure due to such an extreme 

 bathymetrical range as two thousand fathoms ; but undoubt- 

 edly the individuals living at these enormous depths have found 

 their way there very gradually, or ascend and descend from one 

 level to another most leisurelv, so as to become accustomed to 



/ / 



differences in pressure. 



Our information regarding the abyssal realms is far from 

 complete, and our sketch of the natural history of the inhabi- 

 tants of the floor of the ocean should be regarded only as a 

 preliminary outline. Naturally, our knowledge of some of the 

 groups is more extended than that of others, and the results 

 obtained in any one case may differ radically from those reached 

 by the study of less well known groups. As in the history of 

 the fauna of any zoological province, our conclusions are con- 

 stantly modified by the final results derived from a more careful 

 study of some special case. There are of course certain rules 

 applicable to all the inhabitants of the deeper regions, but they 

 are few, and liable to constant modifications from our increasing 

 knowledge. 



