THE LIVING SUBSTANCE. 



103 



tuous in line during contraction. Just so did those more com- 

 plexly organized areas found in the footstalk of VorticellidcC 

 and in the motile appendages of all Protozoan organisms. In 

 a similar manner were bent and made tortuous such Metazoan 

 contractile areas as cilia, and even complex muscle bands, such 

 as the head-attachment-muscle-band in rotifers. There seem 

 to be conditions in which the line of more evanescent contrac- 

 tion waves may be held by the substance for variable periods. 

 There are curious structural relations in the muscle of higher 

 Metazoa which hint that this mode of obtaining more space for 

 mass displacement has been utilised and the protoplasmic differ- 

 entiation organized to increase by minute plications retractive 

 power of the muscular machinery. Nay more, by using the 

 added machinery of jointed endo- and exo-skeletons, such re- 

 tractive plication has been still further increased ; and so the 

 work of economic extension of energy, on the same basis always 

 as that used for the primitive powers of the substance in its 

 initial organizations, goes on. 



[98] To sum up the foregoing : I find an enormous number 

 of true striations and fibrillations of protoplasm over and above 

 those optical and psychological emphases noted by Biitschli. 

 I find, moreover, that while the latter, as lamellar films, ex- 

 press the arrangement and grouping or extension of alveoli ; 

 the former must be characterized as products of actual physical 

 modification, or increment, or organization, of the continuous 

 or interalveolar foam for physiological function. Under this 

 head fall all the host of fibrils and filaments as well as all 

 striations referable to filose or contractile activities of the 

 continuous substance. 



These are therefore to be regarded as substance structures, 

 rather than as basic protoplasmic structure. They are substance 

 tissues and substance organs. 



Contractility. 



[99^] It must be borne in mind that in discussing contraction 

 and its allied phenomena, I speak only of those structures, or 

 areas, or masses, of the substance in which the actual changes 



1 The whole section should be read under this number. 



