42 SCHMIDT ON THE COMPARATIVE PHYSIOLOGY 



est extent : but the fact that the intestinal tube and respiratory 

 apparatus (lung, gill and trachea) are mere inflexions of the outer 

 surface to afford increase of surface, ought to be proved in the 

 Articulata to a demonstration, in addition to other facts, by phy- 

 siology and the history of development ; for in them they entirely 

 consist of that remarkable substance which is characteristic of 

 these animals, viz. chitine. 



Ad c. Wuhler has clearly proved that elimination of oxygen is 

 the ultimate product of the metamorphosis of matter in the Frus- 

 tulicB ; on the other hand, Drs. Schlossberger and Dopping* have 

 proved the exhalation of carbonic acid to occur in Sponges and 

 Fungi. Thus we have the exact antithesis of the required sepa- 

 ration of carbonic acid in animals, and the excretion of oxygen 

 in plants. 



Ad d. I have proved the identity of the substance of the cel- 

 lular membrane of plants with that of the mantle of the Ascidice 

 and FrustuUae, and rendered it probable with that of the Medusce 

 and Polypes. 



II. Reil's position, *'that the vital phaenomena are the result 

 of form and composition," is even now correct when put into the 

 following form : — " The working of the animal machine itself, in- 

 dependent of another sphere of motive phaenomena of a distinct 

 immaterial substance, psychical activity, is the necessary result 

 of the structure and composition of its elements." 



Proof. This is afforded by a comparison of the minute struc- 

 ture of the mantle in the Ascidia with that of plants having the 

 same composition ; not less striking is the systematic position of 

 theCirripeds compared with the relationsof their composition. 



Moreover, the doctrine of Vital Force has gone out of fashion ; 

 a " metabolic power in the cell, " &c. is now substituted for 

 it, i. e. it has received another appellation, or is designated " as 

 the unknown cause of a series of phaenomena which we call life." 

 Every motor phaenomenon is however merely the result of the 

 reaction of at least two masses in motion (the first position in 

 mechanics) ; to explain a motor phaenomenon, and to refer to its 

 causes, means to analyse its intensity and direction according to 

 the parallelogram of the forces of its components : this implies at 

 least two forces ; this is the province of physiology, as well as of 

 every physical science. It is clear that from one primum movensy 

 from one mental phaenomenon (force), assumed as a causal mo 

 * Wbhlcr and Licbig's Annalcii, vol. lii. p. 119. 



