428 Scientific Intelligence. 
quire more special physical conditions for health; others more general 
conditions; and their extent of diffusion varies accordingly. Thus the 
plants of temperate climates are more widely diffused over the surface of 
under similar physical conditions, in different regions of the globe 
pen iicular distribution of plants. Edward Forbes has expressed 
defining five bathymetrical zones, or belts of depth, which he calls,—1, 
Littoral; 2, Circumlittoral ; 3, Median ; 4, Infra-median ; 5, Abyssal. The 
life-forms of these zones vary, of course, according to the nature of the 
sea-bottom ; and are modified by those primitive or creative laws that 
have caused representative species in distant localities under like physical 
conditions,—speties related by analogy. Very much remains to be ob- 
perfect theory. But in the progress to this, the results cannot fail to. be 
practically most valuable, A shell or a sea-weed, whose relations to 
depth are thus understood, may afford important information or wara- 
ing to the navigator. To the geologist, the distribution of 
A A os 
