SEGMENTATION 79 



If the analogy of crystals be set aside and we seek for other 

 parallels to regeneration there are none very obvious. I have 

 sometimes wondered whether it might not be possible to institute 

 a fruitful comparison between the renewal of parts and the refor- 

 mation of waves of certain classes after obliteration. In several 

 respects, as I have already said, some curious resemblances with 

 the repetitions formed by wave-motion are to be traced in our 

 organic phenomena, and though admitting that I cannot develop 

 these comparisons, I think nevertheless they may be worth 

 bearing in mind. When, after obliteration, an eddy in a stream, 

 or a ripple-mark (a more complex case of eddy-formation) in 

 blown sand is re-formed, we have an example in which pattern is 

 reconstituted and growth takes place not by virtue of the com- 

 position of the materials — in this case the water or the sand — 

 but by the way in which they are acted upon by extraneous 

 forces. 



A feature in the actual mode by which ripple-marks are 

 reconstituted may not be without interest in connexion with 

 our phenomena of regeneration. When, for example, the wind 

 is blowing steadily over a surface of fine, dry sand, the familiar 

 ripple-marks are formed by a heaping of the sand in lines trans- 

 verse to the direction of the wind. The heaping is due to the 

 formation of eddies corresponding with positions of instability. 

 When the wind is steady and the sand homogeneous, the dis- 

 tances between the ripples, or wave-lengths, are sensibly equal. 

 If while the wind continues to blow, the ripples are obliterated 

 with a soft brush they will quickly be re-formed over the whole 

 area, but I have noticed that at first their wave-length is ap- 

 proximately half that of the ripples in the undisturbed parts of 

 the system. 12 The normal wave-length is restored by the gradual 

 accentuation of alternate ripples. Of course the sand-ripples are 

 in reality slowly travelling forward in the direction towards 

 which the wind is blowing, and for this our living segmentations 

 afford no obvious parallel, but the appearances in the area of 



12 In the actual case observed, the ripples unsmoothed had a wave-length of 

 about 2^ inches; and when the new ones were first formed, there were about 30 

 ridges in the length originally traversed by 15 or 16. 



