100 



TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



active movements, some of them are often called " water- 

 fleas " (see fig. XII., at 9 and 12). 



The most important group of the Entomostraca is the 

 Copepoda. These little " water-fleas " are exceedingly 

 abundant in the sea, and are of great economic import- 

 ance. It has been calculated that under each square 



Fir;. XIL 



Plankton," or floating organisms from the 

 tow-net (mostly enlarged). 



metre of ihe surface of the Baltic there are one million 

 Copepods, and that these use annually 4,730 millions of 

 the small Ceratium (see before, fig. I.) as food. Herrings 

 feed Largely on Copepoda, and for a square mile of surface 

 water it has been shown that the annual consumption of 



