Causation of Vital Movement. 44o 



Fig. 11. Fig. 12. Fig. 13. 



as a voucher for the truth of the above statement. We see there 

 everywhere the hooks making their appearance with a short and a 

 long claw, like the swivel we hang our watch on in the pocket. 



The voluntary muscles of all vertebrates and of many invertebrates 

 consist of fibres, the contents of which are perfectly regularly dis- 

 posed in layers and transversely striped. For shortness, this striped 

 mass may be called "rhabdia." This it is which has been universally 

 identified with the contractile substance. But it has been ascertained 

 that in many cases the nerve-ending does not come at all into direct 

 contact with the rhabdia, but with another mass, which is highly 

 nucleated and of pap-like softness. This latter is un striped, and has 

 all the appearance of protoplasm. It occurs in very varying quantity 

 under the nerve-antler ; in Amphibia, where the sublemmal nerves 

 run out in a long course, it is not apparent as a separate layer, but it 

 occurs more abundantly in the same measure as the branchings retract, 

 and the field of innervation becomes smaller. At first it is found 

 chiefly between the twigs, in the intervals of the branching, and then 

 in the form of a " sole," which among the much contorted branchings 

 of reptiles and mammals grows thicker, till it sometimes in some nerve 

 eminences forms quite a thick cushion. Since we have succeeded in 

 making the nerve-endings visible in uninterrupted series of very fine 

 sections of mammalian muscle stained with gold, there can no longer 

 be any doubt that the complete separation of the sublemmal nerves 

 from the rhabdia by measurable layers of sole-protoplasm, though 

 not the rule, is yet by no means rare, and that many muscles possess 

 no other sort of nerve-endings than such as these with apparently 

 indirect contact (20). 



It would be difficult to understand why the innervation should 

 have in some muscles, as in the Amphibia, no intermediate layer while 

 having in the majority of cases an interrupted layer, and in others 

 a continuous layer of varying thickness to traverse. But when we 

 consider what the substance of the sole is, of what it consists, how it 

 is distributed, and when we know its origin, it appears that it is 



