32 
boundaries of species^ 
threshold of all useful investigation of these 
subjects, and that is the absolute constancy 
of species. The oak tree for instance, is^ 
under all circumstances, and has been 
through all recorded time, a distinct kind 
of tree having leaves, stem, flower, and 
fruit, differing from all others, and bearing 
seed ‘‘after his kind” alone; and which 
differences though varied in amount by 
cultivation or climate, vet never become 
obliterated or confounded. This is also 
true in the animal kingdom; so that the 
existence of distinct, and constantly distinct 
kinds of living creatures, is to be assumed 
as an ultimate fact in all our reasonings. 
Species thus resemble the alphabetical 
letters ; the type may vary in form, may be 
Roman or Italian, but the character and 
power of the thing signified remain the 
same. 
There are instances of very wide diversity 
produced by circumstances in separate 
individuals of the same family, but it is 
undoubtedly established that such differ¬ 
ences are transient, sometimes enduiing foi 
one generation, sometimes for a longer 
