Fes.,1893. DISTRIBUTION OF MARINE ANIMALS. 93 
though small in comparison to some other groups, is rich enough in 
itself to allow conclusions in faunistic problems. 
The problems of the marine fauna are so varied and numerous 
that we can discuss only a few of them in this place. For con- 
venience, we might divide them into quantitative and qualitative 
problems. It is about the former that the combat between Haeckel 
and Hensen is carried on,7.e., about the uniformity of the distribution, 
and about the foundation which is given by simgle captures to general 
conclusions. It is too early as yet to enter into this question, 
basing conclusions only on the results of single groups, but it 
may be affirmed that everything known until now from the different 
investigators indicates a much more equal composition of the 
Plankton than was supposed even by Hensen himself. It is certain 
that the influence of the coasts extends to a considerable distance, 
that even islands cause modifications, and that currents often change 
the aspect of the fauna almost at once; but Hensen is the first to 
acknowledge the importance of all these factors. 
Setting aside these quantitative problems, there remain the 
qualitative ones, namely, the nature of the composition of the 
fauna with regard to the different species, and the geographical 
occurrence of the single forms. In other words, ave there in the sea as 
as on the mainland aveas of distribution with characteristic inhabitants, or 
(though certainly the coast has zones of life) ave the peculiarly Plankton 
forms universally distributed in it ? Ve know for certain that there are 
forms of life peculiar to the open sea, Plankton animals, far 
excellence, which are cosmopolitan, and which occur both in the 
Atlantic and in the Pacific or Indian Ocean, and in very different 
latitudes. At the last Congress of the German Zoological Society, 
von Graff exhibited such cosmopolitan forms of the group Turbel- 
laria, and von Martens, Spengel, Chun, and others seconded him by 
relating similar facts in the Molluscs, Tornarias, Siphonophores, &c., 
and this led to an interesting discussion as to the probable continuity 
of the two oceans in former ages. Among the Medusz we meet with 
species the distinguishing characters of which are so insignificant 
that we should, without doubt, consider them as belonging to one 
species had they not been found in such different regions. On the 
other hand, we know some forms of Medusz which have been found 
hitherto only in a certain limited district, which occur in this district — 
regularly, but which have never been seen elsewhere. 
Without impairing the fact that there are cosmopolitan forms 
which are as regular iwhabitants of the Atlantic as of the Pacific 
Ocean, it is to be expected a priori that we should find in different 
latitudes at least a different fauna. Since in a different latitude the 
life-conditions undergo a marked change, and show differences in the 
temperature, in the movement of the water, in the weather, and 
so forth, we ought to find a different adaptation and different 
characters. 
