38 



TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



the eggs of most of the edible fishes are hatched as larva-. 

 Figure 13 shows the curve formed by the catches of the 

 total plankton in Port Erin Bay during 1908. 



This Diatom maximum is followed by an increase in 

 the Copepoda (minute Crustacea), which lasts for a con- 

 siderable time during the early summer; and as the fish 

 larva? and the Copepoda increase there is a rapid falling 

 off in Diatoms. Less marked maxima of both Diatoms and 

 Copepoda may occur again about the time of the autumnal 





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Fig. 13. 



equinox. These two groups--the Diatoms (fig. 12) and the 

 Copepoda (fig. 11) — are the most important economic con- 

 stituents in the Plankton. A few examples showing their 

 importance to man may be given : — Man eats the oyster 

 and the American clam, and these shell-fish feed upon Dia- 

 toms. Man feeds upon the cod, which in its turn may feed 

 on the whiting, and that on the sprat, and the sprat on 

 Copepoda, while the Copepoda feed upon Peridinians and 

 Diatoms; or the cod may feed upon crabs, which in turn 

 eat " worms," and these feed upon smaller forms which 

 are nourished by the Diatoms. Or, again, man oats the 



