No. 1.] ORGANIC VARIATION. 255 
while this physio- and morphological correlation of the organs 
aids each organ in the fulfilment of its proper function, it 
simultaneously acts as a restraint upon the exertions of the 
vital processes of the particular organ ; for the particular organ 
does not functionate merely for the maintenance of its own 
existence, but primarily for that of the whole organism, and 
when it has fulfilled the demand of the whole, its correlation with 
the other organs would cause a temporary cessation of its activity. 
Thus the correlation of the organs exerts a restraint, —acts as 
a regulator, upon the amount which each shall perform. And 
when the correlation is perfect, we must assume that each organ 
can normally perform a certain fixed amount, and no more nor no 
less. Since the performance of a physiological function results 
in morphological change, showing the direct correlation of the 
function and structure of an organ, the result follows that, if 
the amount of physiological action performed by an organ is 
determined by the correlation of the organs, the amount of 
morphological change must be determined also by the correlation 
of the organs. This fact is important for the establishment of 
the deduction, which will find its treatment further on, that 
variation can appear only when the complete correlation of the 
organs has been disturbed. And since the degree of perfection 
of the division of labor between the several organs is propor- 
tional to the amount of differentiation of the organism, it is 
correct to conclude, that the completeness of the correlation of 
the organs stands in a direct proportion to the degree of differ- 
entiation of the organism, — the higher the organism the more 
perfect is the correlation of its organs; and vice versa, the 
lower the organism is structurally, the less intimate is this 
correlation, z.c. the more independent the several organs are. 
It will be well here to analyze and compare briefly the ideas, 
progressive and regressive development. Either process may 
modify a given organ in regard to its structure (chemical and 
morphological), its size, position, and, in meristically arranged 
organs, its number. Progressive development tends to com- 
plicate or further differentiate its chemical and morphological 
structure, to change its position and dimensions, and (subject 
to certain limitations) to increase its number in a meristic 
