1 70 The Evolution Hypothesis. 



Each unit is, then, a little universe or infinitesimal 

 microcosm, complex beyond conception. The visible 

 heavens, in the correlations of the solar and astral 

 systems, are simplicity itself compared with the in- 

 tricacy of the correlated motions and equilibrated 

 systems enclosed in each physiological unit. 



4. These units differ in kinds as the developed 

 organisms differ in kinds. They " possess the property 

 of arranging themselves into the special structure of 

 the organism to which they belong." * From the 

 lowest forms of vegetal and animal organizations, to the 

 highest, from the Amoeba to man, immense as are the 

 varieties of organisms, so immense are the varieties of 

 physiological units each of them as completely dif- 

 ferentiated as the perfected structure of the living 

 thing each stamping with its own character every 

 kind of living thing. 



But the incalculable diversity is still greater than is 

 thus indicated: for not only do kingdoms, genera r 

 species, varieties, and all the other recognized groups 

 of organisms, mark divisions among the physiological 

 units, but the differentiation among the units runs 

 clown to the differences which may be seen among^ 

 the children of the same parent, or in growths 

 from the same seed ; not only so, but every organ of 

 the body has its own special kind. The little 

 world of relations and adaptations in a single living 



* Biology, 66. 



