Origin of the chseto-planlLtoii. I propose in another paper to treat of the origin of the
chaito-plankton, and it will there be shown that the diatom, Chcetoceros decipiens, which
constitutes the principal mass of the chteto-plankton, belongs to the west Atlantic area,
or to the cold southwards current along the American coast, and that it is thence con-
veyed by under-currents across the Atlantic towards the Azores and the European coast.
In the month of November, when the superficial strata of the Atlantic are driven away
— or rather become mixed with those beneath — the species above-mentioned appears at
many points between the Newfoundland Banks, the Azores and the mouth of the English
Channel. It multiplies during the winter and is conveyed in the spring towards Iceland,
the Faroe Channel and into the North Sea, whence it spreads towards Spitzbergen.
Other species of the west Atlantic area, which accompany Chcetoceros decipiens across the
Atlantic, such as Calanus finmarchicus, Tlialassiothrix longissima and Ceratium arcticum,
die sooner or later in water of so high a salinity as 35 p. m.
Some species of the temperate Atlantic, such as Oncoea minuta, 0. conifera, Oithona
plumifera, 0. similis, Collozoum inerme, frequently follow the chteto-plankton on its way
towards the north.
Species which accompany the Chaetoceros decipiens into the North Sea. The fol-
lowing species occurred in the North Sea over the whole cha3to area or at least in its
western parts. Some of them are of southern origin, or belong essentially to the styli
and desmo types, others come from northern regions and from Scotland.
Species of northern origin

Calanus finmarchicus,

Metridia hibernica,

Pseudocalanus elongatus,

Temora longicornis,

Cyttarocylis denticidata,

Gonyaulax spinifera,

Chcetoceros borealis var. Brightwellii,

Coscinodiscus oculus iridis,

C. polychordus,

Rhizosolenia semispina.
