SEA-FISHERIES LABORATORY. 175 
It may be (1) that the great vernal maximum which 
dies away in May and June in the Irish Sea passes off 
more slowly further North, and is still found lingering 
on in some parts of the Hebrides, until the end of July, 
or possibly even longer. Or it may be (2) that in some 
of these deep northern channels the Diatoms that else- 
where constitute our vernal maximum remain on in 
comparative abundance throughout the greater part of 
the year. Still a third possible explanation is (3) that 
the Diatoms constituting these July phyto-plankton 
gatherings may have invaded the Hebridean seas from 
the North Atlantic at some period subsequent to the 
vernal maximum. Personally we are inclined to regard 
the first of these three suggestions as the most likely to 
be the correct explanation of the facts we have described, 
but we do not consider that it can yet be regarded as 
established by the observations before us. It is obvious 
that such a matter can only be determined by frequent 
periodic observations carried on throughout the year by 
means of vertical hauls at fixed localities. Such series 
of detailed observations have still to be made in the 
Scottish seas. Mr. George Murray, in 1896, took some 
series of horizontal tow-net gatherings at various 
localities round the coast of Scotland for the Scottish 
Fishery Board, and he published a brief report* the 
following year on his results. His observations were 
made in March, July, August and December, and were 
widespread, including several of the localities we have 
sampled; but they seem to deal mainly, if not wholly, 
with the surface of the sea, and in any case do not include 
vertical hauls in deep water. Murray does not give a 
detailed analysis of his catches, and unfortunately does 
not deal with the zoo-plankton; still it is interesting to 
*S.F.B. Report for 1896, Vol. XV, part ili, p. 212. 
