90 BULLETIN OF THE BUREAU OF FISHERIES. 



of charts portraying the actual distribution patterns of certain species. Unfortu- 

 nately Petersen thought fit to plot upon each of these charts the records for a consid- 

 erable number of species (26 in one case), thus rendering it very difficult to distinguish 

 the distribution of any one of these, and to a large extent impairing the usefulness of 

 the charts. Petersen's "General results" (of which an English translation is provided) 

 includes one of the most philosophical discussions which have appeared of the factors 

 determining the distribution of marine animals. 



The important paper of E. J. Allen (1899) has already been mentioned in an earlier 

 chapter. Allen has, among other things, presented 16 charts, each portraying the 

 distribution of several species, usually members of the same zoological class. Each 

 species is indicated by a letter, its relative abundance at various points being denoted 

 by the style of type. These distributions are plotted upon an identical form, having 

 the bottom characters indicated by conventional shading. Only scattered patches are 

 thus represented, however, and in general the charts have little in common with our 

 own. 



The detailed distribution of numerous marine species has likewise been ascertained 

 by Herdman and his associates for the neighborhood of the Port Erin biological station 

 on the Isle of Man. Seven distribution charts have been published (Herdman, 1901), 

 each chart embracing one or more entire groups of organisms. Upon these charts each 

 species is designated by a number, so that the total distribution of any given form may 

 be ascertained (though rather laboriously) by finding all the' various positions occu- 

 pied by the number which has been assigned to it. 



