x ELECTROMOTIVE ACTION IN NERVE 345 



certain layers of the striated muscle-fibres and the nerve : thus 

 verifying a conjecture long since hazarded by Engelmann (54), 

 when he defined the isotropous ground-substance of the muscle as 

 "a somewhat modified continuation of the axis-cylinder of the motor 

 nerve-fibres," and distinguished it as " nervous " from the " con- 

 tractile " tissue. Biedermann's own (methylene-blue) experiments 

 are little favourable to the assumption of any such intimate 

 relation between the final endings of the ingoing axis-cylinder 

 and the intermediate discs, although he has recently devoted 

 special attention to this point. The most favourable preparations 

 of Crustacea (crayfish), and of several kinds of locusts (Locusta and 

 Acridium), failed to show any such relation. Farther investigation 

 of the point is indispensable. 



Comparison at once suggests itself between the marked 

 difference in the motor nerve-endings of different animals (and in 

 different muscles of the same species), and the differences of 

 function in the same muscles such, e.g., as the sluggishness of the 

 claw- and agility of the tail-muscles in crayfish. The experi- 

 mental data in this direction do not, however, justify any con- 

 clusion. Nor must it be taken for granted that the characteristic 

 morphological differences seen in the parallel axis-cylinders down 

 to their final ending (e.g. in the abductor muscle of the crayfish- 

 claw) actually correspond with the double innervation here ex- 

 hibited from the motor and inhibitory nerves, although such a 

 conjecture is by no means unfounded. 



Information as to the motor nerve-endings in uninuclear 

 striated and smooth muscle cells of vertebrates and invertebrates 

 is still very imperfect. The absence of characteristic end-plates in 

 cardiac muscle, even in the higher vertebrates, is however estab- 

 lished, the character and ending of the finest non-medullated 

 rami being usually such that they branch many times dichoto- 

 mously, and then wind round the muscle-bundles, after which 

 they penetrate into these last, and terminate at the individual 

 cells in very fine, varicose end-branches (Eetzius). The same 

 mode of ending seems to prevail in smooth muscular parts, where 

 again there is remarkable similarity with certain very simple 

 forms of nerve-ending in the striated muscles of low vertebrates 

 and invertebrates. 



I)u Bois-Eeymond affirmed that the major part in the 

 doctrine of muscular innervation devolved upon histology, and if 



