SEA-FISHERIES LABORATORY. 137 
(5) Why do Diatoms appear again in quantity in 
autumn, and why did those of them that differ 
from the spring species not develop in April 
if conditions were then favourable for such 
organisms ? 
(6) Do all the species of the summer and winter 
zoo-plankton remain all the year round in the 
Irish Sea, or do fresh invasions from outside 
occur each season 
Other questions might be stated, but the above will 
serve to show the fundamental nature of the problems— 
some of which involve the life-history and physiology 
of Diatoms throughout the year, and can evidently not 
be solved by an enquiry into the distribution alone. 
Attempts have been made (see especially Jorgensen 
and Nordgaard, ‘‘ Hydrogr. and Biolog. Investigations 
in Norweg. Fiords,’’ Bergen, 1905) to answer similar 
questions in regard to other European seas; but we do 
not discuss these at present, since it is clear that the 
first thing required in connection with our local 
problems is to determine the relations of the Irish Sea 
plankton to that of the seas lying to the north and to 
the south and in the Atlantic outside Ireland and 
Scotland—both on the surface and in the depths. Such 
information will enable us at least to ascertain how far 
our seasonal changes in the plankton are due to 
migrations or invasions from outside. Now while it is 
possible to obtain the necessary information in regard 
to the sea-areas lying to the south of the Irish Sea, as 
the English Channel and the neighbouring part of the 
Atlantic between Ireland, Cornwall and France is being 
thoroughly investigated under the scheme of the 
International Council, no such data are obtainable in 
K 
