TROPICAL PLANKTON. 269 
Herdman’s notes that the water taps to which the tow- 
nets were fixed, received their supply from tanks into 
which the water entered by a valve at a distance of some 
12 feet below the surface of the sea. This necessarily 
restricted the plankton collected to species living at about 
that depth. It is well-known that many animals, and 
particularly Copepoda, haunt chiefly the actual surface of 
the sea, while others are found at varying distances down 
to 100 or even 1000 or more fathoms. 
This uniformity of depth for tow-net work is an unfor- 
tunate necessity of collecting from merchant or passenger 
vessels while maintaining a steady, rapid speed, and not 
allowing of stoppages. ‘The large proportion of fractured 
specimens is another unavoidable drawback in this mode 
of collecting, necessitating much careful manipulation, 
selection, and dissection for unmutilated recognisable 
characters. 
These facts must always be taken into considera- 
tion when dealing with plankton not collected by properly 
equipped vessels fitted out for Marine Biological work, 
when stoppages can be made as desired, and any required 
depth accurately gauged and worked at. 
It is a most gratifying result of the trouble kindly taken 
by Capt. Wyse and Mr. Herdman in making these collec- 
tions, that, as will be seen from the notes on the species, 
almost all show an extension of their hitherto known 
range of geographical distribution. Our further knowledge 
of these minute Crustacea which play so important a part 
both as ocean scavengers, and as themselves a very im- 
portant constituent of the food of fishes and other animals, 
would be largely increased if other navigators would kindly, 
in the interest of science, follow the example of Capt. 
Wyse and Mr. Herdman, and so enable us to have collec- 
tions from all parts of the world. 
