Dec. 1, 1881] 
this anomalous motion has arisen from the action of 
solar tides. Finally we have in this miniature system 
of Mars a foreshadowing of tie ultimate destiny of our 
earth and our moon, 
Do I say the ultimate destiny? Nothing is ultimate in 
nature. The moon and the earth would have come to an 
amicable and a final agreement had they been let alone. 
But now the sun has intervened and disturbed the earth's 
rotation. The truce once broken, the moon again pro- 
duces tides on the earth, the earth reacts on the moon, 
and a whole chain of complicated movements are the 
consequence. I shall not now attempt to trace the further 
progress of events. 
I have dealt with very large figures in this lecture, and 
perhaps I have taxed your imagination by my demands 
that you should conceive of periods of tens of millions of 
years. Yet after all let us look at the results in their true 
proportion, compared with the universe in which our lot 
has been cast. : 
Truly we have been engaged with a very trifling matter. 
Is not our earth one of the most insignificant bodies in 
the universe? And our moon is much smaller still. Nor is 
it even the life-history of our earth that we have been 
considering, it is merely a brief episode in that history. 
What are the periods of time we have been discussing 
when compared with those infinitely longer periods during 
which the solar system has been evolved? Even the 
solar system is but one out of one hundred million such 
systems, each of which has its own life-history. Viewed 
in their true proportions, the phenomena I have described 
are but of infinitesimal importance, and_the time ‘they 
have occupied is merely ephemeral. 
No doubt we have only dwelt upon the tides on the 
earth and the tides in the moon, which have been of such 
infinite importance. But do not suppose- that tides are 
confined to the earth and to the moon. So far as we 
know, every body in the universe is capable of producing, 
and actually does produce, tides in every other body. 
Every planet throbs in response to the tides produced in 
it by every other planet. Every star has a distinct tidal 
wave produced in it by every other star. You may say 
that such tides are infinitesimal, but you must remember 
that infinitesimal causes, sufficiently often repeated, can 
achieve the mightiest effects. 
We know that tides have wrought our solar system into 
its present form; and are we to say that the wondrous 
powers of the tide have no grander scope for their exer- 
cise? I prefer to believe that tides operate far and wide 
through the universe, and that in the recognition of the 
supreme importance of tidal evolution we mark a great 
epoch in the history of physical astronomy. 
POPULAR NATURAL HISTORY? 
Ue present volume of this finely illustrated work 
finishes the account of the Verteprates with the 
history of the Fishes, and gets over as well an immense 
mass of the Invertebrates. The story of the Fishes is 
contributed by Prof. H. G. Seeley, who, in the limited 
compass of 150 pages, of which about one-sixth is occu- 
pied with figures, has given a very fair and comprehensive 
notice of this class. The Fishes are the only primary 
division of the Vertebrata which live in water, and have 
no representatives passing their lives upon land or in the 
air. This condition of existence is probably the cause 
of the close correspondence in bodily form in the majo- 
rity of fishes, which progress through the water chiefly 
by movements of the tail, and use the fins as organs with 
which to steer a path. “Clear as is the idea which rises 
in the mind at the mention of a fish, the multitude of 
forms which fishes exhibit are greater, perhaps, than those 
to be found in any of the other great groups of Vertebrate 
1 ““Cassell’s Natural History.” Edited by P. Martin Duncan, M.B., 
F.R.S. Vol. v., illustrated. (London: Cassell, Petter, Galpin, and Co., 
£881. 
NATURE 
107 
animals described in the previous four volumes of this 
series. The slender form of the lamprey or eel contrasts 
with the expanded body of the turbot or the plaice ; the 
short deep form of the sun-fish is unlike the broad, flat- 
tened, and long-tailed skate ; the sea-horses, when attached 
to sea-weeds by their prehensile tails, at first sight present 
none of the familiar characteristics of fishes. The flying- 
fish, which have the fins so expanded as to serve some of 
the purposes of wings, present a remarkable contrast to 
the spheroidal spiny body of the globe-fish, while the 
hammer-headed shark exhibits a form of body in some 
respects more singular still. When we turn to details of 
proportion and structure, and contrast the shapes of the 
head or of the tail, the variety among fishes is altogether 
exuberant.” 
As an illustration of the woodcuts to be found plenti- 
fully in this volume, we select a sea-horse some time since 
described by Dr. Giinther, the strange dézarre form of 
which will at once attract attention. The illustration is a 
very fair copy of the beautifully-drawn figure of Mr. Ford 
in the Proceedings of the Zoological Soziety of London 
for 1865, and represents, of the natural size, a specimen of 
Phyllopteryx egues from South Australia. “There is no 
doubt,’’ writes Dr. Giinther, “‘ that these fish attach them- 
selves with the prehensile end of their tails to stems of 
sea-weed and other objects; and when they are in the 
vicinity of sea-weed of a similar colour to themselves, 
their resemblance to it must be so great that they would 
easily escape being observed by their enemies.” We fancy 
that Prof. Seeley is wrong in stating that, “as the name 
implies, this fish has very much the aspect of a moving 
plant.” The idea in Swainson’s mind was doubtless 
nearer to the actual meaning of the words he formed the 
generic title from—that of leaf-winged—and we may 
venture to call Dr. Giinther’s species the Leaf-finned 
Sea-horse. 
The section on Fossil Fishes is very short, but a great 
deal of information is contained therein. ‘A large pro- 
portion of fossil fishes belong to the division Palzichthyes. 
This group comprises most of the fishes which have been 
met with in the primary rocks and many of those found 
in the Secondary strata; but in Tertiary deposits the 
Teleostean division is quite as well represented in the 
geological formations as in existing seas. There is no 
evidence of any gradual succession of fishes in the order 
of increased complicity of structure, as the deposits in 
which they occur approach nearer to the present day, and 
there is no reason to suppose that the oldest fishes known 
were the first that appeared upon the earth. The earliest 
fishes discovered were met with in the Lower Ludlow 
rocks, which form the upper part of the Silurian strata. 
The most ancient genus is Scaphaspis, a small buckler- 
headed fish, which had the body covered with scales. 
Many allied genera are found in the overlying Old Red 
Sandstone, in which fishes appear in extraordinary 
variety. Among the allies of Scaphaspis are Pteraspis, 
Cephalaspis, &c., some of which range down to the 
Silurian rocks. Near to these fishes must be placed 
Coccosteus, Pterichthys, and the immense American 
fossil of Devonian age named Dinichthys. These fishes 
are thought to be related to Ganoids and Sharks, but in 
external form they more closely approximate to Loricaria, 
though the tail is heterocercal. They form a distinct 
group named Placodermi.” 
While four volumes and a goodly portion of a fifth are 
devoted to the Vertebrata, there are not wanting signs 
that the immense divisions of the animal kingdom here 
grouped as Invertebrata are to be treated of after the 
usual stereotyped fashion, and that at most one further 
volume will bring this series to a close. The Invertebrata, 
we are told, are divided into great types, or groups, which 
are (1) the Mollusca; (2) the Arthropoda; (3) the 
Vermes ; (4) the Echinodermata; (5) the Zoophyta ; and 
(6) Protozoa. “These great divisions are not exactly 
