802 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
tion of agreement or difference, but are not” accurate 
data that can be used as the basis for calculations as to 
the population of the sea or the exact quantity of any 
material in each cubic metre or gallon or square mile of 
the ocean. 
Some ‘‘ Pume’’ PLANKTON EXPERIMENTS. - 
In the hope of being able to compare the plankton 
strained from a known volume of water with the catches 
made by our usual nets at the same time, we attached a 
hose to the donkey-pump in the engine-room and took 
the following samples by pumping a measured stream of 
93 
water through the smaller ‘‘ Apstein’”’ net, at a variable 
rate but for a fixed time (15 minutes) :— 

No. Date. Station. Rate of pumping. Catch in c.c. 
1 August 20 iB 6 gallons per minute 0:8 
2 3 22 ie 3} 9 0:3 
3 A 23 TTL 74 0-5 
4 - 29 Fleshwick 8 - 0-5 
5 September 8 i 5 aes 0:5 
6 y 9 LE fj 5 0-4 

If we compare the first two of these by reducing 
both to the same rate of pumping, we find the catches 
are in the ratio 8:5; the coarse-net catches for the same 
dates give the ratio 8:5°15. Similarly the last two are 
in the ratio 7:4, while the coarse net on these dates gives 
2:1. So far there seems to be fair agreement. 
In other cases, however, the coarse net results do 
not agree with those from the pump. Thus if we take 
numbers 1 and 5 we get the catch-ratio 4:3, while 
the coarse-net catches on these dates give the ratio 
11°5:3. In this case, however, the fine net results at the 
same time give exactly the same ratio as the pump 
catches. 
