Ads co fige Piodecnd ide Mice ts al Lagu; or i 
DISTRIBUTION OF DIATOMS AND COPEPODA IN THE IRISH SEA. 173 
Spora RuNIANA.—IIT. The Distribution of certain Diatoms and Copepoda, 
throughout the year, in the Irish Sea. By W. A. Herpmay, F.R.S., 
F.L.S., Professor of Zoology in the University of Liverpool. 
(With 21 Text-figures.) 
[Read Ist November, 1917.) 
Part of the work * of the yacht ‘Runa’ for some years previous to 1914 
consisted in taking periedic samples of the marine plankton at various 
localities around Port Erin, at the south end of the Isle of Man, during the 
two most interesting times in the annual cycle—viz., spring (March-April) 
and autumn (July-September). During the remaining months, when the 
yacht was not in commission, plankton gatherings in Port Erin bay were 
taken with great regularity at the rate of six in the week, three at a time on 
two occasions per week, two of the three hauls being horizontal and the 
third vertical. This systematic plankton survey has been continued for fully 
10 years (1907-1917 inclusive), and over 5000 + samples have been collected 
and examined. ‘The general results of this intensive study of the plankton of 
a central area of the Irish Sea have been given in a series of reports $ drawn 
up in collaboration with Mr. Andrew Scott, A.L.S., and others, and published 
by the Lancashire and Western Sea-Fisheries Committee; but the material 
and statistics collected still contain much information which has not yet 
been made use of. It is proposed in the present communication § to deal 
with the records of the occurrence throughout the year in our district of a 
few of the most abundant of the Diatoms and the Copepoda which make up 
the bulk of the phytoplankton and of the zooplankton respectively at those 
periods of the year when they are most abundant. At the time of the 
spring maximum (usually in April or May) a small silk tow-net hauled for 
about 15 minutes through about half-a-mile of the surface water of the Irish 
Sea will usually catch some millions of individual Diatoms (up to a couple of 
hundred millions || on occasions), constituting probably, on the average, some 
999,999 out of each million of organisms in the gathering €. This is almost 
* For Parts I. and IT. of *Spolia Runiana" see Journ. Linn. Soc., Zool. xxxii. p. 163 
(1913), and p. 269 (1914). 
T More precisely 5116, to the end of 1916, 
t Trans. Biol. Soc. Liverpool, xxii. (1908) to xxxi. (1917). 
§ I wish to acknowledge, with thanks, the help I have received in the preparation of 
these plankton records from Mr. Andrew Scott, A.L.S., and from my secretary, Miss 
H. M. Lewis, B.A. Mr. Scott took for me the excellent photo-micrographs of the plankton 
from which most of the illustrations have been reproduced. 
|| Estimated by counting measured samples. 
«| The average of a number of cases where smaller, but still very large, hauls of Diatoms 
were taken is—Diatoms=about 99 per cent. of the total organisms present. 
LINN. JOURN.—BOTANY, VOL. XLIV, Q 
