1894] The Numerical Intensity of Faunas. 759 
High Vitality, for while these terms may not be co-existent 
upon the first appearance of a species they must quickly be- 
come so. A species originates, if we are to accept the Darwi- 
nian hypothesis by reason of its preponderant adaptation to 
new conditions, and if at first that adaptation is tentative or 
accidental, it soon becomes assured and necessary, upon the 
settling down of species and environment into a complete reci- 
procity. We then may expect two similar but contrasted 
stages to succeed this original, initial state, as is seen in the 
subjoined diagram; these stages presenting equivalent numer- 
ical zones, to be followed by two similar and identical stages, 
which in turn precede the extinction of the species. 
Favorable Environment and High Vitality. 
— — na and ó © Unfavorable Environment 
M" T High Vitality. 
prseter Ei o) bier um 
ronm 
Extinction. Extinction. 
The conjecture here delineated shows a species beginning 
under the favoring conjunction of vitality and adapted environ- 
ment, rising in numerical intensity until a weakening of these 
elements sets in, and the species begins to decline in numbers. 
It may decline along a line of lessening vitality with environ- 
ment constant, or, it may decline along a line of increasingly 
hostile surroundings with vitality constant, and it may be 
gue a stage of equipoise may be reached along either 
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