XX Universiiy of Calif ornia I'ublicaiions in Zoologi/ | Vol. 15 



physical and cliemical conditions of the sea. The two commissions, 

 however, especially the German one, have based nearly all their 

 researches upon an assumption of uniformity in the distribution of the 

 smaller organisms over large areas, and the Port Erin Station is to be 

 credited especially with having demonstrated, very completely, the 

 serious error involved in this assumption. Furthermore the two com- 

 missions differ radically from the Port Erin Station, in that the latter 

 is engaged in intensive rather than extensive investigations, and recog- 

 nizes the necessity of frequently repeated hydro-biological observations 

 in very restricted localities. 



The Scripps Institution has followed, in general, the lead of the 

 Port Erin Station, but differs, perhaps most conspicuously, from all 

 three European institutions, in that its primary interest is in pure 

 rather than economic biology. Its methods are based on the conviction 

 that large numbers of somewhat crude hydro-biological observations, 

 rather than precision of apparatus and exact computations of "filtra- 

 tion constants," will reveal the relations maintained between organ- 

 isms and their environments. After such observations are made the 

 data are subjected to rigorous examination. Two methods of treating 

 the field data are used ; the frequency method and the abundance 

 method. 



The frequency method consists in arranging all the biological hauls 

 in order of the magnitude of one of the environmental elements, say 

 temperature ; separating them into groups so that the temperature 

 range in each is the same, say two degrees; and noting the hauls iu 

 any one group containing the particular species under investigation. 

 Then, by expressing the number of these hauls as a percentage of the 

 total number in that group, a mea.sure of the frequency of occurrence 

 of the species within the limits of that temperature interval is 

 obtained. Proceeding similarly with all the other groups, the relative 

 frequency of the species under the different temperature conditions 

 is found. By this means variations in the frequency of the species 

 may be quantitatively compared with fluctuations in the elements of 

 its environmental complex, correlations between the two estal)lished, 

 the reliability of the correlations tested by statistical methods, and 

 ecmclusions of significance drawn. 



The abiindance method is similar in every way to the frecpiency 

 method except that, instead of depending upon the mere presence 

 and absence of the species, the specimens in each haul are counted. 

 Consequently, the average number of specimens per unit volume of 



