314 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



enumerated together. In addition, the larva? and eggs 

 (in the egg-sacks) were counted. For the West Baltic the 

 number of Copepoda throughout the whole year is very 

 similar, and is very high. The average number, inclu- 

 sive of larva?, for ten cubic metres of sea water, was on one 

 occasion 725,900 ; on another 891,000. That is, a litre of 

 West Baltic sea water contains from 72 to 89 of these little 

 Crustacea. The average depth of the West Baltic being 

 20 metres, there are present for every square mile of 

 surface water from 80 to 100 billion Copepoda. The latter 

 number gives a dry weight of 150,000 kilograms. The 

 relation between adult Copepoda, larva? and eggs was also 

 determined. In a thousand specimens the average was 

 134 eggs, 461 larva?, and 405 adults. The time required 

 for the development of an adult Copepod is on the average 

 a week. The birth-rate per week of the year for Copepoda 

 is thus 134 per thousand. Assuming that the population 

 of Copepoda remains fairly stationary, then the death-rate 

 must be about the same. The calculation of the yearly 

 mortality of the Copepoda of the Baltic becomes a simple 

 matter. For 10 cubic metres of sea water, the mortality 

 would be 175,000 per week, or in a year 8,806,500. Death 

 to a Copepod generally implies that it is devoured by a 

 fish or other animal. So that from a consideration of the 

 death-rate of the Copepoda we can arrive at an idea of the 

 food supply of some of our valuable marketable fish. 

 The Clupeida? feed largely on Copepoda. For a 

 square mile of surface water the annual consump- 

 tion of Copepoda can be regarded as approximately 

 975 billion, or for the 16 square miles of the Eckenforde 

 fishery district a grand total of 15,000 billion. A billion 

 Copepoda yield not less than 1,500 kilograms of dry 

 organic substance, so that the 15,600 billion weigh not less 

 than 23,400,000 kilograms. Taking the average weight 



