OE^'ESIS, HEREDITY, AND VARIATION. 277 



Now though the colloidal atoms of which organisms are 

 mainly built, are themselves highly composite ; and though 

 the physiological units compounded out of these colloidal 

 atoms, 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 arrangement into 

 a more stable aggregate than those which have siightly- 

 unlike forms. Among units of this order, as among units 

 of a simpler order, imperfect similarity must entail imperfect 

 polar balance, and consequent diminished ability to withstand 

 disturbing forces. Hence, given two organisms which, by 

 diminished nutrition or increased expenditure, are being ar- 

 rested 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 inci- 

 dent 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-different units from the other, the tendency to- 

 wards 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 be- 

 come again capable of that re-distribution which constitutes 

 evolution. This view of the matter is in harmony 



with the results of observation on the initial stages of develop- 

 ment. Some pages back, it was asserted that sperm- cell and 

 germ- cell severally arrive, before their union, at a condition 

 of equilibrium. Though approximately true, this is not liter- 

 ally true. I learn from Dr AY. H. Eansom, who has investi- 

 gated the question with great care, that the unfertilized ovum 

 continues, for a time, to undergo changes similar to those which 

 the fertilized ovum undergoes; but that these changes, becoming 

 languid and incomplete, are finally arrested by decomposition. 

 Here we find what might be expected. In the first place, an 

 organism which develops germ-cells, is not in a state of mole- 

 cular equilibrium, but in a state of approach to such equili- 



