Willey. — Economic History of Copepods 323 



dinians. Four kinds of plankton gatherings are distinguished 

 by the relative numbers of the leading types (K. Brandt, 1898) 

 as follows : 



1. Peridinian plankton, with excess of peridinians, chiefly Cera- 

 tium, to which a great part of the phosphorescence in northern waters 

 is due. 



2. Diatom plankton, with excess of diatoms, especially Chcstoceras. 



3. Mixed plankton, rich alike in diatoms, peridinians and copepods, 

 occurring in balanced proportions. 



4. Copepod plankton, in which copepods and other animals prevail. 



From a biochemical analysis of mixed plankton it is possible 

 to arrive at some idea as to the relative nutritive values of the 

 organisms. The figures, when reduced to roundness and con- 

 sistency, are of this order: 1 copepod = 125 peridinians = 

 2,500 diatoms. A rich vertical haul through 20 metres of 

 water taken in Kiel Bay on September 28, 1893, contained: 

 273,000,000 diatoms, 11,600,000 peridinians, and 96,000 

 copepods. 



In Canadian waters there is still a wide field for qualitative 

 work which is an essential preliminary to progress. The divi- 

 sion of copepods to which Calanus and Temora belong is called 

 Calanoida. There is another division, not so well known on this 

 side, named Harpacticoida, whose members are only occasion- 

 ally taken in the plankton net, and are more generally found 

 swimming and creeping amongst seaweed. These are particu- 

 larly abundant around Passamaquoddy Bay, where young her- 

 rings assemble in immense numbers year after year and are 

 caught in fish-weirs for the sardine factories. A couple of 

 young herring, 4^/2 inches long, examined recently at the Atlan- 

 tic Biological Station, St. Andrews, N. B., presented stomach 

 contents consisting of newly-ingested copepods, of which har- 

 pacticoids made up more than fifty per cent. Many of them 

 are identical with species found on the northern coasts of 

 Europe, but some are peculiar to the northern coasts of Amer- 

 ica. It is interesting to note that the two leading species of 

 Passamaquoddy Bay are the same as the two most abundant 

 species in Kiel Bay, namely, Idy(Ea furcata and Harpacticus 



