t 
TROPICAL PLANKTON. 265 
net on the overflow pipe—this was especially the case 
with the Amphipoda, Schizopoda, and larger Copepoda. 
As similar specimens were not so much damaged in the 
nets at the tap on the port side, we may conclude that 
little or no damage is received in passing through the 
pump: , 
“With the help of the carpenter I made an estimate 
of the amount of water passing through each of my nets 
during the period of time for which they were set. At 
the tap, when turned on to the extent which I found 
could just enable the water to get away through the nets, 
four gallons passed out in 45 seconds, which is about 
8,600 gallons in the 12 hours. At the overflow pipe I 
found that, on the average, about 21,600 gallons passed 
in the 12 hours, so these overflow nets strained six times 
as much water as did those on the tap. This, of course, 
accounts for the much larger quantity of material usually 
caught by the starboard nets. The difference in size of 
mesh between the two sets of nets also, no doubt, caused 
some difference in the results. A further cause of differ- 
ence was this:—the tap was supplied bya pipe coming 
from a rose inserted near the bottom of the tank, while 
the overflow pipe left the very top of the tank, and so 
carried off the surface water. I noticed frequently that 
the larger animals and the more powerful swimmers, 
such as small fish, Amphipods, Schizopods, and Megalo- 
pas were nearly all caught in the nets at the overflow 
pipe, and I believe that was due merely to the fact that 
they swam nearer to the top of the water in the tank. 
This is an important reason for using the overflow pipe, 
as well as the ordinary taps leading from the tank, in such 
pump plankton work. 
“The four nets were emptied and re-set regularly twice a 
day, at sometime between 8 and 9a.m., and again between 
