VIII.] HOMOLOGIES. 189 



to do more than refer to the beautiful and complex 

 forms presented by inorganic structures. With regard 

 to organisms, however, the wonderful Acanthometrae and 

 the Polycystina may be mentioned as presenting com- 

 plexities of form which cannot be explained except by 

 the action of internal causes. The same may be said of 

 the great group of Echinoderms, with their amazing 

 variety of component parts. If then internal forces can 

 so build up the most varied structures, they are surely 

 capable of producing the serial, lateral, and vertical sym- 

 metries which higher animal forms exhibit. Mr. Spencer 

 is the more bound to admit this, inasmuch as in his doc- 

 trine of "physiological units" he maintains that these 

 organic atoms of his have an innate power of building 

 up and evolving the whole and perfect animal from which 

 they were in each case derived. To build up and evolve the 

 various symmetries here spoken of is not one whit more 

 mysterious. Directly to refute Mr. Spencer's hypothesis 

 as to the effects of surrounding conditions would require, 

 however, the bringing forward of examples of organisms 

 which are ill-adapted to their positions, and out of har- 

 mony with their surroundings a difficult task indeed. 1 



1 Just as Buffon's superfluous lament over the unfortunate organization 

 of the sloth has been shown, by the increase of our knowledge, to have 

 been uncalled for and absurd, so other supposed instances of non-adapta- 

 tion will, no doubt, similarly disappear. Mr. Darwin, in his "Origin of 

 Species," 5th edition, p. 220, speaks of a woodpecker (Oolaptes campestris) 

 as having an organization quite at variance with its habits, and as never 

 climbing a tree, though possessed of the special arboreal structure of other 

 woodpeckers. It now appears, however, from the observations of Mr. W. 

 H. Hudson, C.M.Z.S., that its habits are in harmony with its structure.. 

 See Mr. Hudson's third letter to the Zoological Society, published in the 

 Proceedings of that Society for March 24, 1870, p. 159 ; also Mr. Darwin's 

 reply in the Proceedings for November 1st, 1870. 



