166 



A CENSUS OF THE SEA 



[part IJ 



PlanktoniG organisms in 1 cubic metre of water in the 02)en 

 Mediterranean Sea off Syracuse. 



Total organisms in 1 cubic metre of water = 2,425,665. 



The table illustrates the defect of the older plankton collectings 

 methods. Lohmann estimates that from 28*5 Vo to 88*5 Vo of the 

 smaller organisms escape capture by the quantitative vertical nets. 

 These captures were made in the Mediterranean, which 'is a 

 plankton-poor sea, and it is probably the case that if the same 

 observations had been carried out in the northern seas a greater 

 proportion of the metazoan organisms (Crustacea, &;c.), would have 

 been captured. One sees, however, that the ordinary plankton 

 apparatus, however well adapted it may be for the quantitative 

 estimation of the larger microscopic animals and diatoms, fails to 

 some extent when applied to the enumeration of the total plankton 

 contents of the sea. All the tables hitherto given therefore really 

 underestimate the abundance of life in the sea. 



The larvae of the plankton. The diatoms, protozoa and 

 copepods belong to the permanent plankton. Being adult organ- 

 isms they never enter into benthic or nektic phases. But the 

 ordinary microscopic life of the sea also includes the eggs and larvae 

 of animals and plants which, in their adult stages, either swim 



1 See Chap. X. 



- Flagellates with plant-like mode of nutrition. 



^ Anomalous organisms ("plant-animals"). 



^ Flagellates with animal-like mode of nutrition. 



5 Includes all multicellular animals. 



