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if not indeed altogether, to be explained by the fact that the 
different observers have studied their specimens in different stages 
of contraction. When fully extended, and then alone, the full com- 
plexity of the structure of striped muscle can be realised; with 
slight contraction Flogehs granules disappear, then Dobie’s globules ; 
finally, in completed contraction, the heads of adjacent sarcous 
elements come together, and the fibril is momentarily homogeneous, 
the former complexity reappearing on extension. So far Professor 
Eutherford’s explanation — how does this come into relation with 
the present hypothesis? The doubly refracting portions of the 
mu'^cle-fibrils may, on this view, be regarded as aggregation granules ; 
for these must inevitably exhibit considerable regularity of form 
and arrangement, Avhen we bear in mind that, if we admit the exist- 
ence of muscle-fibrils at all, we imply that these possess a limiting 
surface, — of course tubular in form and ultra-capillary in fineness, — 
and still more so, if we assume with many histologists the existence 
of fixed points afforded by Krause’s membrane.* In short, it is 
attempted to compare the aggregation-granules of a sundew, not only 
with those of an amoeba, but even with those most complex and most 
peculiar differentiations of protoplasm observable in muscular tissue. 
4. Confirmatory Evidence . — The present hypothesis is thoroughly 
in accordance with recent researches as to the nature and composi- 
tion of protoplasm. Thus Brass f distinguishes cells into two 
layers, — the outer sensory, the inner nutritive, and describes 
phenomena which seem at least closely akin to aggregation. 
Our knowledge of the development of muscle also supports the 
hypothesis. Thus, for instance, W agener j: shows that muscular fibres 
at first differentiate from the protoplasm of multinucleate cells, as 
j^erfectly smooth fibrils (“vollig glatte Faden”), with interfibrillar 
substance. Later there arises, as a secondary differentiation, the 
refracting and non-refracting elements (“ Isotropen and Anisotro- 
pen”), which can extend and diminish, also fuse together and again 
separate. In young heart-muscles these come and go under the 
observer’s eye. 
* Cf. Author’s Prel. Note in Zool. Anzeiger, No. 146, 1883. 
t Brass, Zool. Anzeiger, 120, 1882. 
4 G. Wagener, “Ueb. d. Entstehuiig. d. Qiierstreifen auf d. Muskeln,” 
Arcliiv f. Anal. u. Physiol., Anat. Ahtheil, p. 543. 
