340 THE INDUCTIONS OF BIOLOGY. 



Now though the colloidal molecules of which organisms 

 are mainly built, are themselves highly composite; and 

 though the physiological units compounded out of these col- 

 loidal molecules must have structures far more involved; 

 yet it must happen with such units, as with simple units, 

 that those which have exactly like forms will admit of ar- 

 rangement into a more stable aggregate than those which 

 have slightly-unlike forms. Among units of this order, as 

 among units of a simpler order, imperfect similarity must 

 entail imperfect balance in anything formed of them, and 

 consequent diminished ability to withstand disturbing forces. 

 Hence, given two organisms which, by diminished nutrition or 

 increased expenditure, are being arrested in their growths — 

 given in each an approaching equilibrium between the forces 

 of the units and the forces of the aggregate — given, that 

 is, such a comparatively balanced state among the units that 

 re-arrangement of them by incident forces is no longer so 

 easy; and it will follow that by uniting a group of units 

 from the one organism with a group of slightly-diiferent 

 units from the other, the tendency towards equilibrium will 

 be diminished, and the mixed units will be rendered more 

 modifiable in their arrangements by the forces acting on 

 them : they will be so far freed as to become again capable 

 of that re-distribution which constitutes evolution. 



And now let us test this hypothesis by seeing what power 

 it gives us of interpreting established inductions. 



§ 93. The majority of plants being hermaphrodites, it has, 

 until quite recently, been supposed that the ovules of each 

 flower are fertilized by pollen from the anthers of the same 

 flower. Mr. Darwin, however, has shown that the arrange- 

 ments are generally such as to prevent this. Either the ovules 

 and the pollen are not ripe simultaneously, or obstacles pre- 

 vent access of the one to the other. At the same time he has 

 shown that there exist arrangements, often of a remarkable 

 kind, which facilitate the transfer of pollen by insects from the 



