GENERAL BIOLOGY 771 



warm-water and oceanic fish-species to a closer investigation, 

 and for studying them at various seasons. As a means of 

 control and comparison, measuremejits on a large scale, accord- 

 ing to Petersen's method, would be very important. Although 

 our material is very abundant, it is insufficient for the purpose 

 of distinguishing various size-groups among the fishes. That 

 such groups occur among the deep-sea fishes is plainly indicated 

 by our measurements of Cyclothone (see Fig. 473, p. 620), which 

 show a binodal curve for individuals of Cyclothone signata from 

 500 metres, and a multinodal curve in the case of C. microdon. 

 At 500 metres the average size is about 35 mm., and at 1500 

 metres about 60 mm. Perhaps there is another group in 

 depths between the two mentioned. Regarding the meaning 

 of the nodes in these curves I must confess myself ignorant. 



From the coast banks of Africa we have a series of measure- 

 ments of Dentex macropktkalnms, which for the sizes between 

 17 and 24 cm. show a very regular size-distribution of the fish 

 captured. 



Future investigations of the fish-fauna of the coast banks 

 may lead to good results by starting from the study of such 

 forms as occur also in the North Sea, for instance the hake 

 i^Merhcccius vulgaris). Their growth might then be subjected 

 to a comparative study on a long stretch of coast through many 

 degrees of latitude and under exceedingly various conditions. 

 The same method might also be applied in the case of the southern 

 pelagic clupeidae : the sprat, the pilchard, and the anchovy. 



Abundance of Marine Animals 



On dry land we can, to a large extent, examine the yield of 

 the soil, weighing and measuring the crops, and keep count 

 of animals of economic importance. As regards the yield of 

 the sea our experience is merely of a relative kind. From 

 generation to generation a certain amount of knowledge has 

 been accumulated as to the quantities of various fish that have 

 been captured, but the number of animals actually living in 

 the sea is unknown. 



Many scientists have undoubtedly often had to acknowledge 

 that biology would be raised to an essentially higher level, if it 

 were possible to arrive at absolute figures denoting the numbers 

 of individuals inhabiting the sea, instead of merely the relative 

 figures which are now obtained through the study and com- 

 parison of various catches. 



