70 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
Thus, the Diatoms took on an enormous development 
in early spring, and reached their maximum in April, 
then died down during the summer, and rose again (in 
1907) to a second but much less important maximum in 
autumn (fig. 21). It must be borne in mind, however, that 
the species, and to some extent the genera, that formed 
the autumn increase (Chetoceros subtde and species of 
Rhizosolenia) were quite different from those present in 
spring (e.g., Chetoceros contortum and species of T'halas- 
siosira); and also that in 1908 the autumnal rise was 
scarcely perceptible. 
COPEPODA DIATOMS DAMOF LACELLATE S 
l | 
SEPT (i 
oct 
NOV 
DEC | 
PORT ERIN PLANKTON 1907 NUMERICAL PROPORTION OF SOME GROUPS 
Fie. 21. 
From the lst of the total plankton throughout the 
year, reduced to the average per net per day, it is seen 
that the greatest bulk of plankton in the water 1s in April, 
when the total catches in the day reached an average of 
dl c.c. per haul. Other lesser elevations are seen in June 
with 20 c.c. and August with 25 c.c. The catch in some 
individual hauls runs a great deal higher than these 
averages, the top score being the Nansen net on April 4th, 
with 1645 cc. Fig. 22, showing the average haul of 
plankton per month, brings out the great range and the 
remarkable diversity between some adjacent months. The 
spring maximum in the amount of the plankton is clearly 
