The Geographical Journal (Journal of the Royal Geographical Society): Volume XII, No. 2 [‎270r] (42/154)

OCEAN, AND ITS RELATION TO OTHER OCEANOGRAPHICAL PHENOMENA. 133
In those areas where the ocean is occupied by a warm current at one
season, and by a cold current at another season, a periodicity can be
observed in the deposition of the carbonate of lime in the shells and
other calcareous structures of marine organisms, as well as in repro
duction. On the other hand, in the polar and equatorial zones, where
there is a small range of temperature, periodicity in the deposition of
carbonate of lime, or in reproduction, is absent or difficult to recognize.
This comparative absence of massive carbonate of lime shells and
corals in the polar waters, when compared with the abundance of these
lime-secreting organisms in tropical waters, produces a general resem
blance between the marine faunas and floras of the north polar and
south polar regions, which is very striking, although this resemblance
might have been anticipated from the similarity in the physical con
ditions, which, with reference to temperature range, is shown on the
accompanying map. The resemblance here referred to in the animals
of the two polar areas extends frequently to cases of specific and generic
identity, the species and genera not now being found in the intermediate
tropical area.
In the year 1841, Sir James Clark Ross dredged off the antarctic
continent species of animals which he recognized as the same as he had
been in the habit of dredging in equally high northern latitudes, and
he suggested that they might have passed from one pole to the other
by way of the cold water of the deep sea.
When the Challenger first reached the great southern ocean, the
naturalists of the expedition were much struck with the general like
ness of a large number of the organisms captured in the tow nets and
trawls to those found on the coasts of Europe and North America. In
the reports containing the detailed descriptions of species, the specialists
frequently call attention to identical, or nearly identical, species from
high southern and high northern latitudes, which appear to be entirely
unrepresented in the intervening tropical zones. In many cases, for
instance, they have been unable to detect any important difierences
between specimens from Kerguelen and the coasts of Great Britain,
although, from purely geographical considerations, they have given a
new specific name to the southern specimens.*
* Thus Stebbing describes a new species from the Southern ocean (Amphilochus
marionis) which has a great resemblance to Amphilochus tenuimanus of European seas,
remarking that “ altogether the sum of the differences, added to the great distance
between the localities at which the specimens occur, makes it unsafe to place the
northern and southern examples in one and the same species ” (Zool. Chall. Exp., pt.
67, p. 746). Again, Smith describes a new species from the Kerguelen region (Thracia
meridionalis), which, he says, “is the southern representative of the Greenlandic
species, Thracia truncata, and, indeed, differs so slightly from it that it is with con
siderable hesitation I venture to describe it as distinct, being mainly influenced to do
so by the difference of locality ” (Zool. Chall. Exp., pt. 35, p. 69).
Ortmann, speaking of the Decapod Crustacea, says: “Nach dem Stande unserer
jetzigen Kenntniss ist Keine einzige hipolare Art beJcannt ,, (Ortmann, Zoologischen