SEA-FISHERIES LABORATORY. 133 
In the late autumn (September or October) Diatoms 
again appear in profusion, constituting a_ second, 
autumnal, phyto-plankton maximum (Table, col. F) 
usually not so marked either in bulk or in duration as 
that in the spring. The autumnal phyto-plankton dies 
away in its turn, giving place to the scanty winter zoo- 
plankton—the minimum plankton of the year—which 
persists until the reappearance of the Diatoms in spring. 
This periodicity and the contrast between the phyto- 
plankton at one season and the zoo-plankton at another 
are most marked, as may be seen from the following 
table, which gives a summary of three characteristic 




hauls :— 
April Phyto-pl.| August Zoo-pl, oLeRnan 
CRAPTOCCTOSTS fret a see pany- | 14,000,000 —- — 
Rhizosolenta ....ccccesceses — —. 16,000,000 
TRALAS8IOSITA — snceeserccee| 2,000,000 — — 
Mp Gal DintOINs 4, cerseseederese | 16,790,000 16,528,000 
Dinoflagellata’ .:....-........ —- 125 74,500 
SOG tL. 8 dian de ntdesscomees _ 30 — 
POdONE sae ctecvdstaesecceaset -- 20 — 
Total Copepoda...........0.+. 975 3,995 14,127 
Bish Meee seas Sore 16 — — 





Here the April and the September gatherings are 
seen to be equally characterised by the abundance of 
‘Diatoms, which are totally absent in August, and 
September shows Dinoflagellata in addition, and August 
a pure zoo-plankton consisting mainly of Copepoda. 
The seasonal variation in the bulk of the Irish Sea 
plankton is also seen well in curves or other graphic 
representations. The accompanying diagram (fig. 1) 
shows, for example, the curve for the catches of the 
whole plankton in the year 1908, as given by the large 
series of gatherings* extending over every month, taken 
*See Trans, Biol. Soc. Liverpool, vol, xxiii, p, 244, 1909. 
