VIII 



CONDUCTIVITY AND EXCITABILITY OF NERVE 



55 



sions the type of strict dichotomous branching obtains. We 

 could hardly find a better example of this than the abductor 

 muscle of the crayfish claw with its nerves (3). Here the finer 

 trunks invariably contain, within a stratified sheath of connective 

 tissue, two axis-cylinders of very unequal diameter, and stain- 



ill 'If 



.''iii 1 . ! ' : '&$fe.V 





^ >S\ 



K-V, '4^\ 

 ^^.,. fy 



lOi/H' '''.'M "r*? >' -.:^'.^.V -'"i.^v'K^^" 



1 \--'f . '. \ . nEKv' ' \ ' .:' . ^t . '"Tm. *V-' V" "V-l "" 



,! 



riKs': Mft\\;w .' 



|im4^ 



'liV-\'\W-^^ .'> w i '"' '--^"" 



lite! ^r> 



4 i m \\li? Jtx : 



I ;|I||1^,W ;/ " -:;- 



\%fltPK ^^ft^^%^^- 



FIG. 159. Nerve-cords from the costo-cutaneous muscle of a frog injected with methylene blue, 

 showing numerous divisions and Ranvier's crosses. (Ko' Hiker.) 



ing differently with methylene blue. If these are followed down 

 to the periphery, it will be found that both axis-cylinders divide 

 at exactly the same point ; this is repeated at each new bifur- 

 cation, even to the finest branches, so that the number of rami- 

 fications is conspicuously increased (Fig. 150). Both in the 

 central organ and at the periphery, the ratio of magnitude 

 between trunk and branches is remarkable. The dichotomous 



