1893. DISTRIBUTION OF MARINE ANIMALS. 97 
districts required further confirmation in other groups. Meanwhile, 
several of the Plankton investigators seem to have come to similar 
conclusions, and quite recently an interesting paper by Dr. Dahl 
has appeared, which treats of the different species of the genus Copilia 
(Saphirine Copepods of the open sea) and their share in the composition 
ofthe Plankton. Without entering into the quantitative questions, we 
will compare only the results of this author regarding the qualitative 
distribution. 
First we notice that Dahl distinguishes a difference between a 
northern region of the course taken by the expedition and a southern 
one, inasmuch as in the whole district to the north of the Florida Current 
and the Azores no members of the genus Cofilia occur; so it 
appears that the genus Copziza is tropicalor subtropical, as, for example, 
the family Geryonidz among the Medusz. In the remaining part of 
the course he found five different species (it is remarkable that both 
sexes could be recognised, which show, as is well-known, a pro- 
nounced dimorphism), and these five species are distributed in a 
very characteristic manner. Two of them, C. /ata and C. vitrea, appear 
along the whole course from the Florida Current to Ascension, to 
Brazil and back to the Azores; they might be regarded as similar to 
such forms as Aglauva hemistoma among the Meduse. Two other 
species, C. mirabilis and C. media, alternate with one another in their 
occurrence ; media being found in the Sargasso and in the part north- 
wards of it, mivabilis in the southern parts. So these forms seem 
to substitute each other, while a fifth form, C. quadvata, occurs chiefly 
in the warm currents from the Cape Verde Islands to Ascension. 
Dahl suggests rightly that this distribution cannot as a matter of 
fact result from mere haphazard, and he discusses the probable 
reasons of it, the Atlantic currents and the temperature, in an 
interesting manner. 
If we consider, not the simgle species in their distribution, but 
the faunistic picture which results from the simultaneous occur- 
rence of several species, we may distinguish for these Copepods the 
same limits of districts which we have noticed for the Meduse. If we 
look at Dahl’s chart, we see the abundance of species in the district 
from the Florida Current to the Bermudas, where some species of 
the more southern currents occur besides the forms of district 
No. 2; we see that one district shows the species schematically 
expressed a, b, c,d, another a, d, e¢, and a third a, c, d, and so on; 
and we see further that there is a difference between a western 
part of the Atlantic traversed and an eastern part, all of which 
results correspond to what we have found in the group of the 
Meduse. 
Another publication, by Dr. Apstein, deals with pelagic Annelids, 
the Tomopteride and the Alciopida. We find that this author, too, 
can distinguish a northern and a southern region, with the limits 
drawn above. The Alciopide do not occur to the north of 
H 
