SEA-FISHERIES LABORATORY. 331 
our meaning, we should lke to try to make our position 
clear by means of an example and a diagram. 
Let us suppose that the line A. . A (in fig. 16, I.) is 
the normal and undisturbed curve representing the life- 
history throughout the year of the population of that 
organism in a particular locality. It is a small popula- 
tion early in the year, increases to a maximum in summer, 
and dies down again in winter. That curve represents the 
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‘Fic. 16.—L., A...... A, supposed curve of normal life-history disturbed 
’ by the influence of enemies, ‘‘ weather,’’ &c. 
II., the resulting curve due to the effect of all the factors. 
effect of our first factor alone. Some organisms may 
show such a curve under some circumstances, but it is 
probably much more usual for the curve to be affected by 
the two other factors in the following manner. The line 
BB may represent, diagramatically, the inroad made 
upon the supposed population by natural enemies. That 
is an example of the action of our second factor, and such 
