70 EVOLUTION AND THE 
which we include under the word ‘magnetism’ are 
due to particular modes of collocation that have 
been assumed by the molecules of iron. 
Living matter is especially characterized by the 
complexity of its molecules and their state of con- 
tinual intestine movement. This peculiarity, as well 
as other related qualities, make the simplest aggre- 
gates of such matter especially prone to undergo 
those secondary structural re-arrangements which all 
plastic and homogeneous masses of matter are liable 
to exhibit. And although in the case of living 
matter these re-arrangements manifest themselves 
by producing what we call ‘organization,’ still the 
forms and structures which many of the lowest 
organisms tend to assume are entirely referrible to 
the polarity of their molecules—just as the forms 
of crystals are the results of like, though simpler, 
polarities. 
And, speaking generally, the complexity of organ- 
ization attainable by the lower animal forms gradually 
tends to increase as the masses of matter from 
which new forms are to develop increase in size: 
owing apparently to the multiplication of effects that 
may be induced by the production of several series 
of molecular re-arrangements within the larger aggre- 
gates, The changes progress, however, in each case 
till a condition of moving equilibrium is established 
