94 NATURAL SCIENCE. FEB., 
Dana was one of the first to distinguish such geographical 
faunistic provinces in the open sea by drawing thermic (or, as he 
called them ‘‘isocrymal”’) lines on the map, which did not quite 
correspond to the lines of geographical latitude. The observations 
of temperature were made on shore, and the empirical data were not 
very large, but he has taken into consideration the ‘ modifying prin- 
ciples,” currents, &c., and has deduced some good general concep- 
tions for his work on Crustaceans, the distribution of which had led 
him to his ideas. 
As another interesting attempt in this regard, we may mention 
the account given by Brandt in his monograph of the Radiolarians 
of the great oceanic currents in the Atlantic, which he supposes 
to be the most important factors in the distribution of animal 
life in the ocean. It is remarkable that he considers them as 
‘circle streams,’ by the direction of which a large amount of 
pelagic animals are always kept within certain limits, and only very 
few of them can be carried away by the side branches of the currents 
to other currents, temperatures, &c., where they probably perish, 
while the majority remain under their regular life-conditions. But 
the attempts to divide the ocean into faunistic districts are very few, 
whether it is that no such limits have been believed to exist at all, 
or that our empirical knowledge has: not been large enough till now 
to allow conclusions; and we have to wait for the results of many 
explorations till we can obtain an idea about these complicated 
relations. 
The Plankton Expedition, limited as it was in extent, has given 
us some insight at least into a certain part of the ocean, and we may 
draw conclusions from it with comparative security, since the fishing- 
stations were fairly close together, and since improved methods were 
employed, such as, for example, the ordinary vertical net going down 
always to a depth of 400 m. in order to catch the animals which rise 
and sink to avoid the changing influences of the surface at certain 
times. The results which I have obtained in the Medusz have con- 
firmed my conviction that we can distinguish in the ocean certain 
districts of horizontal distribution. 
The Craspedote Medusz can be divided, as is well known, into 
Leptolina or metagenetic forms, which are derived from a polypoid 
stage, and Tvachylina, or forms with a direct (hypogenetic) develop- 
ment through a free swimming planula and actinula stage. As might 
be expected from the places of capture, chiefly lying in the open sea, 
where polyps have scarcely any chance of flourishing, the Trachylina 
form by far the majority of the Plankton Medusz, and the few 
Leptolina which have been discovered always show a relation to 
the coast. It might be interesting to control this advance, as the 
result of life in the open sea, by a comparison with other groups, 
which also have a sessile stage in their life-history. The Narco- 
meduse among the Trachylina being acknowledged by all compe- 
