756 



DEPTHS OF THE OCEAN 



Fish measure- 

 ments. 



a certain law-bound space of time, which varies in different 

 species. These facts form the basis of an important branch of 

 marine research, which possibly more than any other will help 

 us to understand the life conditions of animals. The foundation 

 of this branch of science is mainly due to C. G. J. Petersen^ 

 and H. Heincke. 



In his first investigations Petersen aimed at defining the 

 age of the fish-species occurring in a restricted area, and for 



this purpose he selected 

 a small Danish fjord, 

 the Holbaek fjord, 

 where he attempted to 

 capture all sizes of the 

 various fishes, and 

 measured the length of 

 each one ; he then 

 tabulated these length- 

 measurements for each 

 species in order to 

 study the frequency of 

 the various sizes. Fig. 

 553 shows the results 

 of his measurements of 

 the common vivipar- 

 ous blenny (Zoarces 

 vivipariis). The scale 

 is in Danish inches, 

 and each dot denotes a 

 specimen measured ; 

 males and females were 

 measured separately, 



T. Petersen. i_ ^i_ i j 



where the sexes could 

 be distinguished. I quote Petersen's description of this graphic 

 representation : " If we now consider the females, we undeni- 

 ably find remarkably few of a length between 8 and lo inches ; 

 also there is a marked gap between the largest of the fry and 

 the smallest females. Something similar is seen though less 

 plainly in the males. The latter are, however, too few to let 

 the gaps appear quite plainly. Alternating with these gaps 

 certain sizes occur as it were in heaps, where many fish have 

 almost the same length. The blennies may, to put it shortly, 



C. G 



1892. 



C. G. J. Petersen, Beretiiing fra deit danskc hiologiske Station, No. i, 1890, Kjobenhavn, 



