APP. IV] THE ACCURACY OF THE OBSERVATIONS 311 



North Sea during the spawning season in question. Remember that 

 it is possible that some cod eggs may have been wrongly identified. 



These individual catches are^ : 



Cruise I. No eggs or larvae were taken in 18 hauls. The positive 

 results were 9, 24, 24, 6, 3, 15, 6, 6, 54, 12, 165, 21, 27, 60, 204, 21, 3, 

 3, 3, 36, 24, 6, 9, 48, 21, 3, 15, 21, 108, 69, 3, 36, 48, 12, 18, 9. 



Cruise II. No eggs or larvae were taken in four hauls. The 

 positive results were 3, 9, 12, 24, 15, 216, 222, 183, 96, 156, 168, 543, 

 360, 24, 27, 312, 84, 36, 57, 39, 24, 75, 51, 69, 54, 78, 132, 252, 462, 

 126, 162, 153, 45, 69, 111, 131, 48, 39, 18, 6, 3, 105, 516, 63, 27, 75, 

 15, 12. 



Cruise III. No eggs or larvae were taken in thirteen hauls. The 

 positive results were 3, 33, 83, 29, 140, 60, 98, 71, 45, 44, 19, 9, 19, 

 2, 3, 1, 8, 16, 79, 55, 17, 5, 8, 34, 22, 11, 25, 15, 20, 13, 7, 14, 7, 4, 9, 

 8, 19, 81, 68, 24, 47, 17, 3, 9, 46, 5. 



The reader will find synoptic representations of these catches in 

 the distribution charts and curves in the paper by Hensen and Apstein 

 already quoted. The probable error is discussed by Hensen. Even a 

 cursory glance at the figures given above, with a reference to the 

 chart of the cruises and the positions of the stations, will I think 

 convince the reader that it is not impossible to make a roughly 

 approximate statement of the abundance of all fish eggs in the North 

 Sea which are of the pelagic type ; that is, their distribution is not 

 so variable that an average cannot be made. It may be argued of 

 course that Hensen missed certain spawning grounds, or failed to fish 

 in places where a greater abundance of eggs than was found might 

 have been present, or conversely that he fished in places where there 

 was an unusual abundance of ova. But this is pure conjecture and is 

 ct priori improbable when the distribution of the eggs actually found is 

 considered. The analysis of the catches by well-known statistical 

 Tuethods will shew that there is a certain probable error in the 

 estimate of the number of eggs present per square metre, and so of course 

 in the estimate of the total number of eggs in the whole North Sea. So 

 we may say, as Hensen does, that the actual number present ma}^ be 

 so much less, or so much greater than the number actually estimated. 



Fish eggs have absolutely no powers of locomotion, and larvae 

 practically none, when we consider the size of the area. They are 

 distributed by the mixing of the water due to winds, tides and 

 currents. Thus the zoologists of the Nordsee Expedition found that 



^ Nordsee-Expedition, Tab. vii. p. 40. 



