CONTENTS xi 



the catch — The Stempel-pipette— Validity of the Hensen methods— The 

 objections of Haeckel and Kofoid — Lohmann's investigations — Other quanti- 

 tative plankton methods — Capture of plankton by appendicularians — Defects 

 of the Hensen methods 117 



CHAPTER VII. 



THE DISTRIBUTION OF THE PLANKTON. 



The mixing of the plankton in the sea — Experimental errors in the Hensen 

 methods — Vertical distribution of the plankton — Stratification of the plankton 

 — Heliotropic migrations — Changes in the distribution of the plankton due to 

 temperature, viscosity and convection currents — Inshore and offshore plankton 

 — Plankton types — Oceanic and neritic plankton — Distribution of the plank- 

 ton according to hydrographic conditions — Atlantic and North Sea plankton — 

 Cleve's investigations — Plankton mixtures — Halistatic planktons . 142 



CHAPTER VIII 



A CENSUS OF THE SEA. 



Difficulties and uncertainties of the estimation of the life of the sea — 

 Density of the plankton of the North Sea — Average plankton contents of the 

 North Sea — Abundance of diatoms, peridinians and copepods in the sea — 

 Variations in the density of the plankton with the locality — Density of the 

 micro-plankton— Density offish-eggs and larvae in the sea— Hensen's "Nordsee 

 Expedition" of 1895 — Absolute abundance of certain species of fish in the 

 North Sea — Errors in the estimations — Density of life on the sea bottom 157 



CHAPTER IX. 



THE PRODUCTIVITY OF THE SEA. 



Productivity of the North Sea — Produce of the North-Western fishing area 

 — Productivity of an inshore fishing area — Productivity of the shell-fisheries 

 of the West coast of England — Cultivated water areas — German carp fisheries 

 - -A cultivated mussel fishery — The absolute productivity of a sea area — 

 Composition of marine produce — Relative productivity of the sea and the land 

 — The impoverishment of the sea — Productivity of the sea in different 

 latitudes 178 



