ARE NERVES EVER "DIFFUSED"? 71 



gained by declaring that the nervous tissue is in a " diffused 

 state." This is making an assumption, and concealing it in 

 a phrase. If I were to declare that gun cotton contained 

 nitre, because gunpowder contains it ; and if, when my state- 

 ment was answered by repeated analyses proving no nitre to 

 be there, I were to rejily, "the nitre may not be detected by 

 your analysis, because it is in a diffused state," you would 

 shrug contempt at such chemistry. But this is precisely 

 analogous to what is done daily with respect to nervous 

 tissue. Men assume that all animals must have nerves ; 

 if the nerves are not visible, it is because they are "diffused." 

 Now, this reasoning is not only vicious as logic, it is par- 

 ticularly vicious in Biology, where structure is of equal 

 importance with composition. Nerve is a specific thing, 

 having a specific composition, and a specific structure ; to 

 talk of this thing as " diffused," is to talk of it as wanting 

 one of its constituent characters ; it is like talking of fluid 

 crystals, or square circles. All this Dr Williams, I am sure, 

 would be the first to admit, for he doubts the existence of 

 nerves even in the Echinodermata ; and I would ask him 

 whether the tentacles of the Terehella are not assumed to 

 have muscles, in accordance with the current notions that 

 wherever there is Contractility the existence of muscles 

 must be inferred ? I put the question as a question merely. 

 My own observations utterly failed to detect muscular fibres 

 in the tentacles of the species I examined. On one occasion, 

 indeed, they presented the aspect of circular fibres, which I 

 thought must be the muscles Dr Williams refers to ; but, 

 on applying a power of 800 diameters, these fibres resolved 



