A PRIORI VIEWS. 389 



consciousness;^' yet we are often really little better 

 when we persist in constructmg the forms of the simpler 

 animals according to the analogies of our own structure, 

 instead of directly observing what Nature presents to 

 us. No sooner do we perceive certain manifestations 

 of Sensibility, than we at once conclude the presence of 

 a nervous system ; no sooner have we a glimpse of a 

 nervous system, than we are apt to conclude it to be 

 the same in structure as our own. In like manner, 

 Contractility is supposed to imply the presence of a 

 muscular system ; and the muscles of the lowest ani- 

 mals are supposed to be only minuter forms of the same 

 organs found in man. But dkect study of Nature 

 assures us that there may be Sensibility without nerves, 

 and Contractility without muscles ; it further assures 

 us that the nervous and muscular structures, when 

 present, differ greatly in different forms of the animal 

 series ; and that we must understand these differences 

 if we would understand Physiology, The law of unity 

 of composition, when rightly understood, is a guide of 

 great value ; but it is too often a will-o'-wisp, luminously 

 misleading, We get into the habit of naming organs 

 according to a general idea of their functions, instead 

 of keeping the idea of special function dependent on 



To quote the emphatic language of one who has given his life to this 

 subject : " Our knowledge even of the coarser framework of the nervous 

 system is still too much in its infancy to permit us to venture^ with any 

 success, on the construction of theories respecting the functions of its 

 various elements." — Stilling, Uebe^' den Ban, der Nerven-primitivfaser 

 u. d. Nervenzelle, 1856, p. 7. 



