MARINE BIOLOGICAL STATION AT PORT ERIN. 71 
due to a great and sudden increase in the amount of 
Diatoms present (see fig. 21). The other rises seen later 
in the year, as in June, August, and to a slighter extent 
in October, are less marked, and are less clearly due to 
one cause. 
The hauls taken on an off-shore station, on April 5th, 
show the condition of affairs during the spring maximum 
of the Diatoms, when 14 millions of one species, 
Cu 
aé 
eo et 
Jon Fel. Mer Ahr May dune Joly Avg Sept. Oct Now Dec 
Fic. 22. Diagram showing average haul of Plankton per month in 1907. 
Chetoceros contortum, were present in one haul of the 
Nansen net. The total number of Diatoms in that haul 
was nearly 17 millions, including two millions of 
Thalassiosira nordenskioldii. Comparatively few Cope- 
poda and other organisms were preseat. The two surface 
gatherings of this date were moderately alike, the same 
organisms were present in both, although one net had, 
in some cases, about twice as many as the other; but still 
