OF A NERVOUS SYSTEM. 181 



But, Tvlien to these observations upon the simplest 

 creatures are added, the positive facts demonstrated 

 by me with reference to ultimate distribution of the 

 finest nucleated nerve fibres and their bioplasts, in a 

 number of tissues of vertebrate animals, an amount 

 of evidence is appealed to, which ought not to be 

 disregarded. The conviction forced upon the mind 

 is irresistible, that in their general structure, ulti- 

 mate arrangement, and mode of action, the nerves 

 of difierent classes of animals from the highest to 

 the lowest, and the nerves distributed to all the tissues 

 of the same animal exhibits so many points in common, 

 that we may conclude the arrangement is the same 

 in principle in all. The active part of every peri- 

 pheral nerve apparatus is an uninterrupted network 

 of extremely delicate fibres, which are structurally 

 continuous with the masses of bioplasm in the nerve 

 centres. These last, however, in the lowest classes 

 being as it were so spread out as to render it difiicult or 

 impossible to define which part of the nervous system 

 should be considered peripheral, and which central. 

 The arrangement is such that it might be correctly 

 described as consisting of multitudes of closed circuits 

 which are uninterrupted, and are structurally con- 

 tinuous in every part. 



In many terminal organs, no doubt, the appear- 

 ances are such as to justify upon superficial exami- 

 nation the conclusion that the nerves really form 

 true ends. In many instances it has been distinctly 

 afl&rmed that one single nerve fibre was lost in a 

 single terminal cell or other organ ; and as regards 

 striped muscle it has been stated as a fact of observation 

 that such is the case, by a large number of observers. 

 If this were so, we should be compelled to conclude that 

 the single nerve fibre was really terminal. But in 

 eveiy single instance in which I have had the good 

 fortune to obtain good specimens of such organs, I have 

 been able to detect more than one nerve fibre. At the 



