SEA-FISHERIES LABORATORY. 183 
Whether the species regarded as characteristic in 
the first and third of these areas be really ‘‘ oceanic ”’ 
in the sense of having been carried in from the open 
ocean, or not, at any rate there is a real difference in the 
prevalent plankton which can be exemplified by the 
following selection of typical species :— 

‘““QcEANIC”’ SPECIES | ‘‘ NERITIC”’ SPECIES ‘“OQCEANIC”’ SPECIES 
FROM THE CLYDE FROM THE SEAS FROM N. oF SKYE. 
Sea AREA. ROUND MULL. 
Chaetoceras boreale, Biddulphia mobiliensis. | Rhizosolenia semispina. 
C. criophilum. Chaetoceras constrictum. | Peridinium sp. 
Rhizosolenia alata, C. curvisetum, | Ceratium spp. 
R. semispina. C. debile, C. didymum. Calanus helgolandicus.* 
Peridinium sp. Kucampia zodiacus | Pseudocalanus elongatus. 
Ceratium spp. Lauderia borealis. | Oithona similis. 
Calanus helgolandicus.* | Leptocylindrus danicus. 
Pseudocalanus elongatus.| Thalassiosira gravida, 
T. nordenskioldi. 

We would point out that this is no case of 
distinguishing merely a region characterised by mero- 
planktonic species (which spend only a portion of their 
life in the plankton) from neighbouring seas containing 
holo-planktonic organisms (which live all their lives 
in the plankton). The species we have given in these 
three lists are all of them holo-planktonic,t equally 
unconnected with the sea-bottom at all stages of their 
existence; but there is general agreement that those in 
the central column inhabit coastal waters, and that the 
other two series are usually found in the open ocean or 
in water which there is reason to believe has recently 
come from the ocean. It is not necessary to suppose that 
all the individuals of the oceanic species have actually 
* This is not affected by the fact that Calanus and some other 
Oceanic Copepoda live on all the year round in deep water close to 
land, such as at the entrance to Loch Fyne. 
We do not regard the fact that a Diatom’s resting-spore may 
sink to the bottom and remain for a time in a dormant condition as 
sufficient to constitute that Diatom a mero-planktonic species, 
