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 

 of the 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 Copilia occur ; so it 

 appears that the genus Copilia is tropical or subtropical, as, for example, 

 the family Geryonidse among the Medusae. 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. lata and C. vitvea, 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 Aglaiiva hemistoma among the Medusae. 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. quadrata, 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 single 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 Medusae. If we 

 look at Dahl's chart, we see thfe 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 

 Medusae. 



Another publication, by Dr. Apstein, deals with pelagic Annelids, 

 the Tomopteridae and the Alciopidae. We find that this author, too, 

 can distinguish a northern and a southern region, with the limits 

 drawn above. The Alciopidae do not occur to the north of 



H 



