ii CHANGE OF FORM IX MUSCLE DURING ACTIVITY 157 



the number of fibres in which waves occur grows less and less, 

 and after a time there are only a few, in which they spread 

 at longer and longer intervals, until finally they appear in single 

 fibres at very remote periods." 



Since, as Eollett also affirms, the first, slowly - spreading 

 waves appear in fibres that are still capable of total contractions - 

 (twitches), it cannot be doubted that the short waves also must 

 be regarded as " peculiarly distributed processes of movement 

 in normally active muscular substance, produced by specific 

 excitation." These waves in the muscles of dying Corethra- 

 larvse, present the greatest similarity with the movements of 

 freshly-excised insect muscles, as frequently observed since the 

 researches of Bowman (20). Eollett studied these in long, 

 narrow strips of muscle from a great number of beetles, in which 

 the undulatory movement often lasted for hours. It usually 

 reaches its maximum development at the first moment, where 

 the particles of muscle are quickly examined under the micro- 

 scope. Here, too, the waves appear as short knots rising and 

 falling steeply, and spreading slowly in the fibres, and their 

 length also is limited, including only from about 12 to 24 striae. 

 This limitation continues when the undulatory motion becomes 

 less energetic, which happens again in this case, because the 

 waves appear in fewer and fewer fibres at longer intervals, and 

 finally only at prolonged periods in single fibres. If freshly-excised 

 beetle muscle is covered quickly and examined under the micro- 

 scope, a lively undulation is seen to be spreading over the fibre, 

 but we are, as Eollett says, quite ignorant as to the cause of the 

 undulations. They spread along the fibres, coming and going 

 always in the same direction. Yet this is not invariably the 

 case. Sometimes a definite starting-point of the advancing wave 

 occurs in the middle of the individual fibre. This was demon- 

 strated by Bowman, and later by Aeby, on the transparent legs 

 of certain small kinds of spiders. A swelling appears on the 

 given point, which (cf. Aeby) appears to rest for a moment on 

 the crest of its progress, and then suddenly divides in such a 

 way that the most swollen part sinks rapidly back to the original 

 level, while the two halves separate and spread in opposite 

 directions towards both ends of the fibre ; where such a spot has 

 once been found, it is easy to see that it forms for some time 

 a permanent starting - point for new, periodic undulations. 



