Causation of Vital Movement. 



445 



movement the richer they are in sarcoglia, as in the case of the 

 red mnscles, nucleated and rich in glia, which contract more slowly 

 but with greater power than the white muscles poorer in glia which 

 are quick and spring-like, and also the sluggish embryo muscles, in 

 which glia predominates because as yet but little protoplasm has 

 been converted into rhabdia; and further the cells of unstriped 

 muscle-fibre, which are wanting in the regular transverse striation, 

 and contain, as it appears, besides more abundant glia, an elastic 

 material of special form and arrangement. 



The hypothesis would be overthrown if contractile fibrils were 

 found in which no sarcoglia was to be detected. But even in the finest 

 fibrils of Stentor, the structure of which Biitschli (22) has recently 

 elucidated, we must hold the significance of punctated transversely 

 penetrating indentations to be protoplasmic, and we can therefore 

 scarcely expect ever to find a contractile thread in which nothing- 

 whatever should be found of the primitive contractile material such 

 as it everywhere exists. 



Of late this view (23) has been defended from the purely morpho- 

 logical side (24), on the strength, namely, of the very fine reticular 

 structure of protoplasm to which more attention is being paid, and 

 which is demonstrable on objects of all grades of organisation. Proto- 

 plasm, in fact, is not so formless as at first appeared, but shows a 

 structure comparable with nothing better than w 7 ith the appearance 

 presented by a transverse section of muscle with its glia framework 

 stained with gold. We may expect that these reticular structures, who.se 

 consistency appears to vary extraordinarily, will some day lead to the 

 establishment of a fruitful hypothesis of the inner mechanism of 

 protoplasmic movement, in place of that held hitherto which affords 

 no glimpse into the essence of vital mechanical work. 



Compared with this larger problem, that of the causation of vital 

 movement appears the more accessible of the two, the latter being con- 

 sidered as a physiological inquiry after the constitution of the normal 

 stimulus by which work is done. Perhaps, indeed, the answer is to 

 be looked for from the most perfected organisation of muscle, where 

 the initiatory process is localised by a distinct nerve-ending, rather 

 than from the primitive organisation where the excitation may 

 set in at any place, and lies in the protoplasm itself. We know dis- 

 tinctly that the muscle-wave begins in the field of innervation, for 

 we have long seen the natural contraction in the interior of trans- 

 parent insect larva) starting from the nerve eminences. We know 

 this also from the experiments of Aeby, who followed the muscle-wave 

 myographically from the nerve-line onward, and now we are able to 

 display the beginnings of the contraction as local thickenings at the 

 point of attachment of the nerves caught and fixed by sudden harden- 

 ing. Since the nerve grasps the muscle in a restricted region it 



