46 THE AMEBIC AN NATURALIST [Vol. XLVII 



2. The general distribution of each member of a 

 "couplet" is never entirely coincident with that of the 

 other, but varies from a contiguous and overlapping 

 to a radically isolated distribution, according to the 

 ' ' couplet. ' ' 



3. Each species occurring in the San Diego region has 

 its own definite and specific manner of vertical distribu- 

 tion just as truly as it has its own specific morphological 

 characteristics. 



4. Those San Diego species having the most similar 

 vertical distribution are those possessing the most dis- 

 tinctive morphological characteristics or, to st&te it 

 otherwise, the morphological difference between species 

 is inversely proportional to their distributional dif- 

 ference. 



5. Whenever two or more species have been obtained 

 in the same haul, never more than one was representd by 

 sexually mature individuals. 



6. With one or two possible exceptions, the mature 

 specimens of each species occur in different strata of 

 water. 



On the basis of these facts we are forced to conclude 

 (a) that the more closely related species of Cluetognatha 

 are isolated from each other either horizontally, ver- 

 tically or by virtue of physiological differences causing 

 fertilization to take place in different strata of water, 

 and (b) that "Jordan's Law" is only partly true, when 

 tested by vertical distribution, for, while the more closely 

 related species do not inhabit the same environment, 

 they do inhabit the most remote environments. 



Aside from these obvious conclusions the primary 

 significance of this paper is that of emphasizing the need 

 of more exhaustive and quantitative data relative to or- 

 ganisms, on the one hand, and their environments, on 

 the other, before any solid basis can be had upon which 

 to build theories regarding the operation of isolation, 

 adaptation, natural selection, mutation and other fj 

 supposedly concerned in the evolution of species. 



