28 EVOLUTIONS OF ORGANIZATION. 
of modern science.” Rather, I apprehend, the 
method of true science, modern or not, would be to 
study each evolution separately, attending to all the 
phenomena, and investigating its limits, and the 
action of every possible factor in its production. 
Thus, truly, it is of importance to study the opera- 
tion of.circumstances of environment at the present 
day, that we may understand the effects of environ- 
ment in the past; and science is enormouslyindebted 
to Darwin for the stimulus which he has given to 
that inquiry. But just as in the evolution of lan- 
guage, although environment plays an all-important 
part, the fundamental factors are the existence of 
ideas to communicate and a parallelism of things 
of different order, rendering it possible for ideas to 
be represented by signs, so also in the evolutions of 
organization there is a non-material element in the 
definitely directed impulse, and there is a physiog- 
nomic propriety in organic forms, a class of facts 
appreciated by both Oken and Dana, telling of 
spirit which pervades the whole. 
It is certain that the evolutions of form after 
passing through periods of activity do cease; for 
while all the most curious forms of invertebrate 
life——polyzoa, echinodermata, lamellibranchs, brach- 
iopoda and cephalopoda, are formed already in 
palzozoic times, the vertebrates have in the same 
