On the Relation of the îsotropous to the anisotropous Layers in striped Muscles. 543 



of Striped muscles might be explained as strands of protoplasmic sub- 

 stance differentiated from the sarcoplasm by often repeated strains 

 brought about by the attraction of rows of small masses of nuclear 

 substance for the intervening layers of protoplasmic substance, — a 

 proposition which is as simple as it is probable. 



One further point deserves notice : if contraction is brought about 

 by the flowing of the isotropous layers into the anisotropous, Krause's 

 discs could, I think, be explained as the optical expression of some 

 differentiation produced by the strain which would take place at that 

 point, as shown in the diagram Fig. 31 (cf. Eimer 1. c). This suggestion 

 receives some support from the occasional finding of similar discs in 

 Hensen's clear bands, such as I have found and figured (Fig. 25, 30). 



From the foregoing the following provisional conclusions seem 

 warranted : 



1) The isotropous layers retreat into the anisotropous. 



2) This retraction is alone sufficient to account for muscle con- 

 traction. 



3) There is a certain amount of positive evidence tending to show 

 that the anisotropous layer is a mass of nuclear substance. 



I cannot then help thinking that Schäfer's photographs and Ver- 

 worn's general theory of protoplasmic movements have advanced and 

 materially simphfied our conceptions of the morphology and physiology 

 of that long-standing enigma, striped muscle. 



Explanation of the table. 



Table 29. 



Fig. 1. Muscle of Apus, showing a wave of contraction: above, 

 it is fully expanded ; in the middle, is the homogeneous or transition 

 stage ; and below is the inverse or fully contracted stage ; cf. Fig. 9, 

 which is an isolated fibril of the same. 



Fig. 2. A muscle of Branchipus, showing a wave of contraction, 

 from full expansion above to the homogeneous stage below; cf. Fig. 14 

 which is an isolated fibril of the same. 



Fig. 3. A fully contracted muscle of Branchipus, the fibrils of 

 which are in the inverse stage: showing the sarcoplasm drawn together 

 longitudinally, and the chromatin threads springing out from between 

 the fibrils. 



