KINDS OF NERVE FIBRES. Ill 



in the bioplasm, never ceases for a single moment from birtli 

 todeath"("Biopl.,"p. 167). 



In many of the lower animals, e.g., the common starfish, and 

 some other members of the radiata, are seen very delicate 

 fibres and masses of bioplasm, arranged so as to form an ex- 

 tensive network amongst the tissues, and the entire " nervous 

 system" consists of such a network extending through all parts 

 of the organism. Dr. Beale is convinced that an arrangement 

 fundamentally similar in principle is common to all animals, 

 from the highest to the lowest : " The active part of every 

 peripheral nerve apparatus is an uninterrupted network of ex- 

 tremely delicate fibres, which are structurally continuous with 

 the masses of bioplasm in the nerve centres these last, how- 

 ever, in the lowest classes being, as it were, so spread out as to 

 render it difficult or impossible to define which part of the 

 nervous system should be considered peripheral and which 



" The nerve fibres composing the nerve trunks, and those 

 finer branches which unite to form dark-bordered nerve fibres, 

 may be arranged in the following subdivisions, according to 

 their distribution : 



" 1. Nerve fibres passing towards a centre Afferent 'fibres. 



"2. Nerve fibres passing from a centre .Efferent fibres. 



" 3. Nerve fibres connecting nerve centres with one another 

 Commissural central fibres. 



" 4. Nerve fibres connecting the peripheral ramifications of 

 nerves and peripheral nerve organs with one another Com- 

 missural peripheral fibres" ("Biopl.," p. 182). 



The first three of these subdivisions are in agreement with 

 general opinion, but the last leads to the question whether the 

 nerves terminate by free ends in other tissues, or in certain 

 end-organs, or on the other hand constitute closed circuits by 

 looped extremities. On this possibly hangs the whole theory 

 of the nature of the vis nervosa as a current force, so his expo- 

 sition must be given somewhat fully. 



"The active part of the nerve fibre in adult vertebrata in- 

 variably consists of a very delicate compound thread, which 

 exhibits a slightly fibrous character, and is composed of an 



