78 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
number by the latter date. The adult Copepoda in all 
numbered only 1,045 on the Ist, while they reached 
27,790 by the 14th: younger forms and Nauplii had also 
become much more abundant. By November, however, 
the Diatoms were back in quantity, and Copepoda had 
begun to decrease. 
The Dinoflagellata rose to a maximum in April, 1907, 
after the Diatoms; and may have a second period of 
sudden increase in the autumn if weather conditions are 
favourable. They appear to have been more abundant in 
September in 1908 than in 1907, and, in fact, to have 
maintained relatively high numbers from April through- 
out the summer. 
Ceratium tripos is the most abundant species of Dino- 
flagellate in the Irish Sea, and is present practically 
all the year round in considerable abundance (up to 7,753 
per haul) at the Isle of Man. Our 650 gatherings in 1907 
showed C. tripos on 492 occasions. 
The curve for Ceratium tripos agrees in general with 
that for the total Dinoflagellates, but differs markedly 
from those both of Diatoms and Copepoda. ‘The spring 
maximum in the Dinoflagellates is later than that of the 
Diatoms, but precedes that of the Copepoda. Then, 
again, the September hump of the Dinoflagellates is earlier 
than that of the Diatoms, and much earlier than the 
October maximum of Copepoda. On the whole, the 
annual curve for the Dinoflagellates les intermediate 
between those for Diatoms and Copepoda. | 
Sagitta 1s present throughout the year; it is most 
abundant in August, and the minimum occurs in winter 
(January to March). As showing the difference produced 
by a larger net of wider mesh, we find that during April, ' 
when the hauls with the ordinary tow-nets were giving 
units and tens, those taken at the same time with the 
