SEA-FISHERIES LABORATORY. 187 
present carried out, together with the most valuable 
information which will be afforded by the extensive series 
of observations now being made by the Irish Department 
of Agriculture and Technical Instruction, should enable 
us thoroughly to understand the physical conditions of 
the Irish Sea basin. Unfortunately, reliable fishery 
statistics, the collection of which is in other hands, are 
much more difficult to obtain. | 
We have seen that the minor temperature changes 
are set up by the translocation of masses of water of 
different temperature. Because of the strong tidal 
streams the precise delimitation of isothermal water areas 
in the Irish Sea is rendered most difficult. If it were 
possible to make very numerous simultaneous temperature 
observations over the eastern half of the Imish Sea we 
should certainly find scattered “islands ”’ of cold or warm 
water here and there over the inshore region. Obviously, 
the small, rapidly occurring temperature variations, such 
as those indicated in figs. 11 and 12 
by the heating or cooling of the sea in setu, but are due 
, are not occasioned 
to the transference of comparatively large volumes of 
water from place to place. 
There can be no doubt that the irregular distribution 
of the plankton of the Irish Sea, within the twenty-fathom 
contour-line, is to be traced to these movements of masses 
of water. This must obviously be the case with regard 
to those planktonic organisms which are pelagic stages 
of demersal animals: crab and sea urchin larvae, for 
instance, which are produced at one place and carried 
elsewhere by the movement of the water. Truly plank- 
tonic organisms, such as diatoms and copepods, especially 
such neritic forms as are indigenous to the Irish Sea area, 
probably segregate themselves in bands or zones cf 
relatively great area 
Noctiluca, for instance—and these 
