REVIEWS. 
51 
has been collected to make a volume of the proper size, they will be at once 
printed, bound together, and issued with provisional title-pages and prefatory 
matter. Thus, while the work is in progress, the published part will always 
be in a state fit for reference, and those who choose may keep it always in its 
original form ; but on its completion, fresh title-pages, tables of contents, &c., 
will be issued, in order that the different memoirs may be brought into 
regular systematic sequence, according to the nature of their contents. An 
inconvenience which would naturally arise from this rearrangement, namely, 
the loss of all indications of date of publication, has been obviated by a very 
simple plan, — each separate memoir will have its own number as part of the 
report on the Zoology of the Challenger Expedition, and each sheet will have 
at the foot of its first page the indication of the part to which it belongs and 
the date of publication of that part. Volume I., now published, contains six 
parts, thus numbered consecutively. 
In his general introduction to the Challenger Reports on Zoology, with 
regard to which, he says, he must be considered only in the light of the 
Editor of the whole work, Sir Wyville Thomson describes the general 
objects and arrangements of the Expedition very much in the same terms as 
in his previous book, giving an account of operations in the Atlantic, and 
then proceeds to discuss generally the nature and distribution of the fauna of 
the deep sea. The abyssal region extends, according to him, from a depth of 
500 or 600 fathoms to the bottom of the deepest abysses, and so far as the 
results of recent explorations go, there is no bathymetrical limit to the exten- 
sion of life downwards. At the same time, from the Challenger's dredgings 
it would appear that the abyssal fauna is richest between 600 and 1000 or 
1200 fathoms, below which depth there is a gradual falling off, although 
living organisms were procured from the greatest depth at which the dredge 
was used. From 2000 fathoms downwards, however, the fauna usually be- 
comes more sparse. 
With regard to a matter of considerable interest, namely, the asserted 
absolute darkness of the abysses of the ocean, we are glad to see that Sir 
Wyville Thomson speaks with some reserve. He says, ‘ So far as we can 
judge, direct sunlight does not penetrate to great depths ; ’ and he assumes 
that in the case of those abyssal fishes which have greatly developed eyes, 
those organs have been exaggerated to catch the last feeble rays of light 
coming from above. The notion that deep-sea animals see by the phospho- 
rescent fight emitted by thousands of their neighbours, he dismisses as 
altogether untenable, although he believes that abyssal creatures are phos- 
phorescent in their native abysses, which does not appear to us to be proved. 
The striking uniformity of the abyssal fauna everywhere, due, of course, 
to the equally striking uniformity of the conditions of life, leads Sir Wyville 
Thomson to regard it as representing a very ancient fauna, and in this 
respect no doubt he is right ; but we are by no means inclined to accept the 
inference that therefore the present oceans are of great antiquity. Continuity 
of conditions in such a case does not at all of necessity imply identity of 
, place ; and we can quite conceive of the occurrence of an absolute continuity 
of abyssal conditions, without the assumption that since the close of the 
Palaeozoic epoch, as seems to be implied by Sir Wyville Thomson, the great 
oceanic depths have approximately held the same position on the surface of 
