2 
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; 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 leisurely, 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 anyone case may differ radically from those reached 
by the study of less. well known groups. As in the history of 
the fauna of any zoölogical 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. 
THREE CRUISES OF THE “BLAKE.” 
