THEIR RELATION TO EACH OTHER 



8S 



species it means that this abundance is normal, and 

 that the natural adjustments are such as to maintain 

 that abundance in relation to its food unless man in- 

 terferes, and the results of such interference will be the 

 subject of further discussion, later. The important 

 point is that a species abundant in number of specimens 

 has become so in spite of the combination of all its 

 natural checks and, condi- 

 tions remaining equal, will 

 maintain itself in the same 

 ratio, just as a rare species 

 barely maintains itself 

 against the combination op- 

 posing it. It happens again 

 and again that a common 

 species becomes more than 

 usually abundant, and it oc- 

 curs occasionally that a 

 species normally rare escapes 

 from its control and makes 

 its mark as an injurious 

 form. But even without 

 human interference this 

 rights itself in a season or 

 two: the common species 



may even be reduced for a time to less than its usual 

 numbers, while the rare species drops back out of sight 

 of all but the collector. The checks or natural enemies 

 of neither form ever increase sufficiently under normal 

 conditions to do more than restore the original ratio. 

 What then are these checks that prevent with such 

 absolute effect any undue increase of a species despite 

 enormous reproductive powers? They are really very 

 numerous and of decidedly unequal effect on the dif- 

 ferent forms. We have weather, disease, insectivorous 



dyiduct 



Vegine 

 Oyipositor 



34. — Ovaries of a bee show- 

 ing the different parts. 



