GERMAN PLANKTON INVESTIGATIONS. 313 



journey, in the middle of the North Sea 230 eggs per 



square metre were found, on the Scottish side 275, and 



at another time 130 eggs per square metre. 



The results of Hensen and Apstein for the North Sea 



in 1895 are of interest. Three journeys were made. 



A lasted 8 days, and 1,029 sea miles were covered (in Feb.), and 49 catches 



made. 

 B ,, 9 ,, 1,077 ,, ,, (in Feb. &Mar.) ,, 50 „ 



C ,, 8 ,, 1,291 ,, ,, (in April) „ 59 ,, 



In the journey A the number of eggs and larvae per 

 square metre was 1,932, in B 6,538, in C 6,975 ; total 

 15,495 in 167 catches, eggs and larvae being absent 

 in nine catches. The average per square metre is 

 therefore 92*5 eggs and young fish. This compares 

 favourably with the Baltic average of 37*3. Estimating 

 the surface area of the North Sea to be 547,623 million 

 square metres, this gives a grand total for the North Sea 

 of 148 million fish eggs and larvae. After applying 

 certain corrections and omitting Ammodytes' eggs and 

 larvae, as not being those of food fish, Hensen came to 

 the conclusion that the North Sea during the year 1895 

 contained 157 billion eggs and larvae. This number, being 

 calculated from eggs and larvae actually counted, must be 

 regarded as too small. 



Finally the Hensen method is of practical importance, 

 inasmuch as it enables us to determine during which 

 months of the year certain fish spawn. By means of this 

 net Hensen, on one of his earlier Baltic expeditions, dis- 

 covered that the sprat egg is, in contradistinction to that 

 of the herring, pelagic. The spawning places and number 

 of spawning individuals of the different species can also 

 be approximately determined, since above them the float- 

 ing eggs will be met with in the spawning season in large 

 quantities. 



With regard to the Copepoda, all the species are 



