STRUCTURES RESEMBLING ORGANIC GROWTHS. 169 



The comparison with ciliary movement may with advantage 

 be pursued somewhat further. In the living structure the con- 

 tinuance of the vibratory movement has been shown in many 

 instances to be dependent upon the presence of the so-called 

 basal particle (or "blepharoplast"), which is also the center 

 out of which the structure grows in its development; severance 

 of the ciliary filament from its base instantly arrests the move- 

 ment. 1 A connection between the conditions of contractile 

 activity and those of growth is thus shown; both processes 

 depend upon changes taking place in the basal granule, which 

 represents a specially modified portion of the protoplasmic surface 

 layer, differing in chemical composition from other regions of 

 the cell-surface (as shown by its staining reactions), and pre- 

 sumably also in electrical potential. This connection becomes 

 intelligible if we assume that (just as in the above inorganic 

 model) the basal particle represents an area from which a 

 supply of formative and energy-yielding material flows out along 

 the filament to replace the material which is altered or consumed 

 at each ciliary stroke. This flow of material is to be regarded 

 as associated with an electrical current, which being interrupted 

 intermittently causes intermittent polarization-effects, with re- 

 sultant variations of surface-tension producing the contractions. 

 It is clear that a constant renewal of substance is necessary to 

 maintain the integrity of the cilium and to furnish the energy of 

 its contractions; and the resemblance between these structures 

 and the artificial filaments described above appears to be too 

 close not to be based upon some fundamental identity in the 

 conditions of both their origin and their activity. The wide 

 distribution of these vibratile cellular outgrowths, ranging from 

 the lowest unicellular organisms to the highest animals, as well 

 as the readiness with which they are formed at the free surfaces 

 of cells, indicates that some general and simple condition deter- 

 mines their formation, and also that the conditions of their 

 formation and of their contractile activity are closely connected. 2 



1 Cf. Peter, Anatomischer Anzeiger, 1899, Vol. 15, p. 271; Verworn, Pfluger's 

 Archiv, 1890, Vol. 48, p. 149. 



2 The fact that bioelectric variations in other active tissues (nerve, muscle) are 

 so frequently ihythmical in character is significant in relation to the problem of 

 the conditions of ciliary movement. It is possible that a rhythm or intermittency 



