934 E. A. Schäfer. 



at the expense of the clear substance, and at the same time comes 

 nearer to the transverse membranes. 



6. In extension the reverse process occurs. The tubules become nar- 



rower and longer, and the hyaline substance passes from them 

 into the clear intervals. With excessive extension the sarcous 

 elements tend to separate into two, and eventually perhaps into 

 four series (principal disk with Hensens stria, and accessory disks 

 of wing-muscles). 



7. The sarcomeres are united together end to end to form longi- 



tudinal columns which extend throughout the whole length of the- 

 fibre (sarcostyles, muscle-columns of authors, fibrils of older authors). 



8. These columns are separated from one another laterally by inter- 



stitial or inter-columnar substance (sarcoplasm) which is made 

 very manifest by acid or by gold staining, and has been described 

 by many authors as a reticulum. 



9. In the wing-muscles of insects the sarcoplasm is everywhere in 



large amount: it contains the nuclei and appears to be the remains 

 of the original protoplasm of the muscle -cell. 



10. In most other muscles the sarcoplasm is in relatively small amount, 



but is increased near the ends of the muscle-segments where it 

 forms transversely disposed accumulations encircling the segments. 

 In cross-section these accumulations of sarcoplasm give the effect 

 of transverse networks. 



11. The sarcoplasm is entirely passive, but since it occupies all the 

 interstices of the contractile muscle-segments, it is liable to 

 undergo changes in its arrangement corresponding to the changes 

 in form which the segments undergo when they contract or be- 

 come extended. 



12. The accumulations of sarcoplasm which occur in the ordinary 

 muscles, produce considerable modifications in the optical appear- 

 ances ( cross-striation) of those muscles, both in the extended and 

 in the contracted condition. 1 ) 



University College. London, October 1890. 



*) Besides the papers by more recent authors which have been mentioned in 

 the text I have had occasion to refer to many others which have not been specially 



