MUSCULAR CONTRACTION 325 



study of the individual cases. The streaming seems to 

 take the simplest course in Didinium. Here an extension- 

 current starting from the internal opening of the oesophagus 

 would explain the circulation, if it appeared on the whole 

 possible to refer the streaming movements of the endoplasm 

 of Ciliata to an extension-current of so simple a nature. 



(m) Possibility of an Explanation of Muscular Contraction 

 in this way 



On the other hand, I should like to point out that 

 the above-discussed causes of the changes in shape, and the 

 displacements in the alveolar framework, seem to me to 

 indicate a future explanation of the contraction of muscle 

 fibrils. Although it 

 is not my intention, 

 as has already been 

 remarked before, to 

 enter more closely in 

 this work into muscle 

 cells, the structure of 

 which requires much 

 more accurate clearing 

 up before a satis- 

 factory explanation of 

 their contraction is 

 to be thought of, rig. 22. 



I will nevertheless 



refer briefly to this case.^ Let us imagine as simple a 

 muscle fibril as possible, consisting only of a single row 

 of protoplasmic alveoli arranged one behind the other, which 

 are enclosed in the usual protoplasm, the sarcoplasm, of 

 the muscle cells. The accompanying Fig. 22 is intended 

 to represent a short extent of such a muscle fibril (//), 

 together with the contiguous sarcoplasm, in longitudinal 



1 In 1888, in my Protozoa, p. 1317, I had already pointed out the possi- 

 bility of an explanation of miisoular contraction, in the way which is set forth 

 rather more accurately in the sequel here. 



