314 DARWINISM STATED BY DARWIN HIMSELF. 



an earth-worm, to be highly organized ? If it were no 

 advantage, these forms would be left, by natural selection, 

 unimproved or but little improved, and might remain for 

 indefinite ages in their present lowly condition. And 

 geology tells us that some of the lowest forms, as the 

 infusoria and rhizopods, have remained for an enormous 

 period in nearly their present state. But to suppose that 

 most of the many now existing low forms have not in the 

 least advanced since the first dawn of life would be ex- 

 tremely rash ; for every naturalist who has dissected some 

 of the beings now ranked as very low in the scale must 

 have been struck with their really wondrous and beauti- 

 ful organization. 



Nearly the same remarks are applicable if we look to 

 the different grades of organization within the same great 

 group ; for instance, in the vertebrata, to the co-existence 

 of mammals and fish — among mammalia, to the co-exist- 

 ence of man and the ornithorhynchus — among fishes, to 

 the co-existence of the shark and the lancelet (Amphiox- 

 us), which latter fish in the extreme simplicity of its 

 structure approaches the invertebrate classes. But mam- 

 mals and fish hardly come into competition with each 

 other ; the advancement of the whole class of mammals, 

 or of certain members in this class, to the highest grade 

 would not lead to their taking the place of fishes. Physi- 

 ologists believe that the brain must be bathed by warm 

 blood to be highly active, and this requires aerial respira- 

 tion ; so that warm-blooded mammals when inhabiting the 

 water lie under a disadvantage in having to come contin- 

 ually to the surface to breathe. With fishes, members of 

 the shark family would not tend to supplant the lancelet ; 

 for the lancelet, as I hear from Fritz Miiller, has as sole 

 companion and competitor on the barren, sandy shore 

 of South Brazil an anomalous annelid. The three lowest 



