100 University of California Fuhlications in Zoology. [Vol.8 



one acquainted with Hensen's (1895) "Methodik der Unter- 

 snchimg" knows how excellently this difficult and laborious work 

 has been done. 



From these important researches the "Kiel school" has 

 drawn conclusions of vast significance which, however, are based 

 on insufficient data. One illustration is enough. On the basis 

 of 167 hauls made during the early spring of 1895 in the North 

 Sea, Hensen and Apstein (1897) estimated that the surface 

 waters contained 157,000,000,000 fish eggs. From a knowledge 

 of the average number of eggs annually produced by each 

 species these authors state that the number of mature food fishes 

 in the North Sea may be estimated. As pointed out by Herd- 

 man (1906) this estimate is based on one successful haul (only 

 158 of the 167 hauls made contained fish eggs) for each 3.465,- 

 968,354 square meters, or approximately 133,800 square miles, 

 of the sea. Concerning this estimate Johnstone (1908, p. 168) 

 says: "Such an investigation presents few^er difficulties than 

 are encountered in other quantitative researches." Probably 

 Johnstone (1908) has reference to difficulties in calculating 

 filtration capacities and various coefficients of correction for the 

 nets used, but will even the simplest calculation justify such a 

 "collossal conclusion" when based on only one haul from each 

 133,800 square miles of the sea ? 



Obviously the reliability of such results depends on uni- 

 formity in distribution of plankton over a large area. Are we 

 warranted in assuming that this uniformity exists? Concerning 

 this Herdmau (1906, p. 35) says: "On the West Coast of Scot- 

 land I have seen large Copepoda so abundant for a mile or two 

 that they seemed from the deck of a yacht to be dancing in 

 crowds in the water .... in a few minutes we passed out of 

 the swarm." Again (p. 36) he says: "In the Red Sea and on 

 several occasions in the Indian Ocean I have seen Trichodesmium 

 erytiiraruni forming a most conspicuous red-brown or tawny 

 yellow-brown scum on the surface of the sea for, it might be, a 

 few hundred yards up to a mile in width, and several or even 

 many miles in length, while the sea at each side of the patch was 

 entirely free from the organism." It is unnecessary to quote 

 the numerous similar instances noted by many naturalists. Their 



