228 SAECOLEMMA. 



not contain bioplasm in their ultimate fibrillae, there 

 is good reason for concluding that there is no living 

 matter in the substance of the higher forms of con- 

 tractile tissue. The phenomenon of contractility 

 characteristic of this class of tissues is therefore pro- 

 bably due to changes in non-living formed material 

 only, and is not in any way dependent for its mani- 

 festation upon bioplasm. 



267. Sarcolcmma. The sarcolemma of muscle 

 appears as a transparent tube composed of very 

 delicate membrane, figs. 1, 3, PL VI, p. 222, which is 

 thick in old and fully formed muscles, but very thin 

 in young muscular fibres, while during development, 

 and in the case of some forms of adult muscular 

 tissue (heart, tongue) , no sarcolemma can be detected. 

 Upon its outer surface the sarcolemma is connected 

 with the delicate intermuscular connective tissue, 

 with capillary vessels and nerve fibres, and in insects 

 the trachse are adherent to it, and in some cases are 

 almost embedded in its substance. The greater num- 

 ber of the masses of bioplasm on the surface of the 

 sarcolemma of the muscles of vertebrata are those of 

 the numerous nerves and capillary vessels distributed 

 to the elementary fibre. These are extremely 

 numerous upon the sarcolemma of the elementary 

 muscular fibres of small rodents, as the mouse, but 

 they are seen in connexion with the sarcolemma of 

 almost all muscles. The masses of bioplasm, which 

 I have proved belong to capillary vessels and nerves 

 distributed to this tissue, have been generally re- 

 garded as " connective tissue corpuscles," and the 

 same erroneous conclusion has been arrived at con- 

 cerning the masses of bioplasm belonging to vessels 

 and nerves distributed to many other tissues, and 

 essential to their formation, growth, and action. 



The sarcolemma of the muscles of insects is a very 

 complex structure, in which air tubes or trachae and 

 excessively minute nerve fibres ramify in immense 



