222 REPORT ON ALBATROSS MOLLUSCA CALL. 



The inevitable conclusion is, therefore, that all the animals living 

 under these conditions must have their tissues so constituted as to per- 

 mit the free permeation of the water through every part in order that 

 the pressure may be equalized. How this is possible without putting 

 an end to all organic functions is, perhaps, the greatest mystery of 

 abyssal life. How can a large egg, like those of various deep-sea ani- 

 mals, pass through the stages of segmentation and development, with 

 every molecule of its structure in actual contact with ordinary sea water 

 and every solid particle subjected to a pressure of, say, a thousand pounds 

 to the square inch ? Such questions are much easier to ask thau to 

 answer ; in fact, no attempt at an answer has, so far as I am aware, ever 

 been offered to biologists. 



The looseness of tissue necessary to such a permeation is conspicu- 

 ous in abyssal animals, whose flabby and gelatinous appearance when 

 they reach the surface is notorious. It is, perhaps, most noticeable in 

 the fishes, which, nevertheless, are often armed with formidable teeth; 

 but, under the great pressures of the deeps, it is quite conceivable that 

 each of these loose and half-dissolving muscles may be compressed and 

 reduced to a condition resembling steel wire, and that the organization 

 thus sustained may be as lithe and sinewy in its native haunts as its 

 shallow- water relatives are in theirs. 



It is well known how great an influence on the distribution of shal- 

 low-water species is exerted by the temperature of the water in which 

 they live. No doubt the differences of temperature affect the nervous 

 system, the rate of muscular contraction and the motions of the cilia, 

 by which in mollusks many of the functions of life are aided or wholly 

 carried on. 



But it is probable that the influence of temperature is far more effect- 

 ively exerted upon the development of the ova, and hence upon the 

 propagation of the species, than directly upon the parents. It is prob- 

 able that most adult mollusks could endure a very wide range of tem- 

 perature if the individuals were subjected to the changes by extremely 

 slow degrees; but it has been shown that a difference of one or two 

 degrees below a certain point on the thermometric scale will destroy 

 the embryos of Ostrea or prevent their development, so that they per- 

 ish. In this way the spread of the species may be effectually checked, 

 though the adult shell-fish may flourish without difficulty in the same 

 region. 



In the shallower parts of the Archibenthal Region a few great cur- 

 rents like the Gulf Stream may reach, for a small part of their course, 

 the ocean floor, aud sweep it clean of sediment and detritus if not en- 

 tirely of living beings. Such mechanical effect as is produced mustbfc 

 of a rather steady and uniform nature for considerable periods and iu 

 no respect resemble the crushing and grinding which take place on 

 every exposed beach on which the sea rolls up. In fact, regarded as 

 individuals, the mollusks in the path of the Gulf Stream and other 



