^9©3] 



TABULA TWA ' SCHEME 



27 



slips and in quick apprehension of tlie results. One has but to make trial of the 

 scheme to be convinced. In tabulating, the slips may be quickly arranged and 

 re-arranged as often and in as many ways as is desired for the purpose of securing 

 facts or of testing hypotheses. 



In case but few species are involved a suggestive method is to prepare the 

 diagram on a sufficiently large scale and to place in each area the names of the 

 species and varieties inhabiting it, noting how their distribution agrees with their 

 systematic relationships. If the species are too numerous for names to be used, 

 check-list numbers may be substituted, in different colors for different groups of 

 species. 



A more detailed statement of the distribution may be secured by dividing each 

 square area into nine sub-areas (see diagram) and indicating these respectively, 

 according to points of the compass, as central (C), north-central (NC), northeast 

 (NE), east-central (EC), etc., parts of the area ; N, E, S, and W indicating the 

 series of three sub-areas in those portions of each area, MC for the meridian 

 central or median series and ZC for the parallel or zonal central series. If 

 preferred for the sake of brevity, instead of letters, these sub-areas could be 

 indicated by numbers (arranged vertically, so that sub-areas bearing the same 

 number would have the same relative position in wide and narrow areas). 



A further step would be the use of abbreviations or other symbols for the 

 zones and regions, enabling the distribution to be expressed by formulae : — thus 

 the zones may be indicated by Roman numerals, I to VII, upward from the 

 Tropical; and the regions by A, B, C, etc., (perhaps omitting I, owing to its use 

 for the tropical zone), beginning on the Atlantic side, or the Pacific, as seemed 

 preferable. Thus the distribution of a species known only from the upper Austral 

 zone of eastern Nebraska would be represented by III G 5 (or III G c). The use 

 of numerals would be preferable for brevity, letters would aid the memory. In the 

 narrower areas, having their greatest extent from north to south, an east and west 

 division into but two series of six sub-areas would probably be preferable to one of 

 three series of nine. This sub-division could be carried to a much greater extent 

 if found advisable. 



Let us glance at another possibility. Suppose it were desired to make a study 

 of the distribution of the 11,000 beetles of North America, or, indeed, of the entire 

 fauna and flora of the country, with details of distribution of each of its component 

 groups:- — by using punched cards (instead of marked or tinted slips) in an auto- 



