48 ON GOETHE'S SCIENTIFIC RESEARCHES. 



able certainty which parts correspond to each other. 

 Groethe himself said this very clearly : he says, in speaking 

 of the vertebral theory of the skull, c Such an aper^u^ 

 such an intuition, conception, representation, notion, idea, 

 or whatever you choose to call it, always retains some- 

 thing esoteric and indefinable, struggle as you will 

 against it ; as a general principle, it may be enunciated, 

 but cannot be proved; in detail it may be exhibited, 

 but can never be put in a cut and dry form.' And so, or 

 nearly so, the problem stands to this day. The difference 

 may be brought out still more clearly if we consider 

 how physiology, which investigates the relations of vital 

 processes as cause and effect, would have to treat this 

 idea of a common type of animal structure. The science 

 might ask. Is it, on the one hand, a correct view, that 

 during the geological periods that have passed over the 

 earth, one species has been developed from another, so 

 that, for example, the breast-fin of the fish has gradually 

 changed into an arm or a wing? Or again, shall we 

 say that the different species of animals were created 

 equally perfect that the points of resemblance between 

 them are to be ascribed to the fact, that in all vertebrate 

 animals the first steps in development from the egg can 

 only be effected by Nature in one way, almost identical 

 in all cases, and that the later analogies of structure are 

 determined by these features, common to all embryos ? 

 Probably the majority of observers incline to the latter 

 view, 1 for the agreement between the embryos of dif- 

 ferent vertebrate animals, in the earlier stages, is very 

 striking. Thus even young mammals have occasionally 

 rudimentary gills on the side of the neck, like fishes. 

 It seems, in fact, that what are in the mature animals 

 corresponding parts, originate in the same way during 

 the process of development, so the scientific men have 

 1 This was written before the appearance of Darwin's Origin of Specie*. 



