502 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
correlated with the red and brown tints of the majority of deep-sea 
organisms. 
Some deep-sea species are of gigantic size, when compared with their 
shallow- water allies. For example, some of the hexactinellid Sponges 
are 3 or 4 ft. in diameter, the hydroid Mondcaulus is 3 ft. high, the legs 
of some Pycnogonids extend for over a foot on either side of the body, 
and the largest Echini and Isopods are found in deep water. Sir Wy ville 
Thomson was of opinion that from the Silurian period to the present day 
there had been, as now, a continuous deep ocean w T ith a bottom tempera- 
ture oscillating about the freezing point, and that there had always been 
an abyssal fauna. Dr. Murray thinks, however, that it is much more 
probable that in palaeozoic times the ocean basins were not so deep as 
at the present, that the ocean had then a nearly uniform high tempera- 
ture throughout its whole mass, and that life was either absent through- 
out all the greater depths, or represented only by bacteria, as in the 
Black Sea at the present day. 
Separation and its Bearing on Zoo-Geography.* — Mr. A. E. Ort- 
mann has a notice on a recent publication of his f on animal geography. 
In this work he points out the importance of the principle of separation 
or isolation as affecting the distribution of animals, as well as the origin 
of species. Mr. Ortmann is not one of those who believe that natural 
selection is sufficient to explain the origin of species. He urges that 
the transformation of the species in time is entirely different from the 
differentiation into several contemporaneous species. The former 
process, known to some as mutation, has not been properly understood 
by most zoologists. The author says he cannot enough emphasise that 
mutation of one species in time should not be confounded with differen- 
tiation into co-existing species. The latter process he thinks he has 
demonstrated to be duo to separation or isolation. Separation keeps 
particular groups permanently under particular conditions, and thus 
they are prevented from migrating from one station of definite conditions 
of life into others with other conditions. The chief differences in 
districts are due to the conditions of light, medium, and substratum, 
which the author distinguishes in this kind of way : — “ (1) Light. The 
medium is air; Substratum present — Terrestrial district.” Dealing in 
the same way with four others he forms a fluvial district, a littoral 
district, a pelagic district, and an abyssal. These are practically the 
most important life districts, and, as a rule, every form of animal alive is 
restricted to one of them ; they have existed since dry land rose above the 
surface of the ocean. Not only the differences of life-districts effect sepa- 
ration of the inhabitants, but within each life-district separate parts are 
present. The differences here referred to are what is called facies ; this 
factor, the author thinks, is not yet considered properly in palaeontology. 
Although the geological development of many groups of animals in suc- 
cessive strata has been investigated, no attention has been directed to the 
influence of the conditions of life upon single forms, and the influence 
of separation of these conditions upon the differentiation of particular 
directions of development. In more recent geological times another 
factor, causing separation, is added — the climatic differentiation of the 
* Amer. Journ. Sci., ii. (1896) pp. 63-9. 
f ‘Grundziige der maiinen Tiergeographie,’ Jena, 1896. 
