RELATIVE STABILITY OF LIVING MATTER 317 



cut is made regeneration begins at that point and completes the 

 part. Spallanzani reports that all four legs and the tail of a sala- 

 mander were removed as many as six times within three months, 

 and were regenerated each time, as promptly the last time as 

 the first. He calculated that in all 647 new bones were formed. 



This shows that regeneration not only begins at the proper 

 point, but, in some cases at least, is capable of indefinite repeti- 

 tion. The restored part is at first smaller than the normal, but it 

 continues to grow until the proper size is reached, when it stops. 



If a part of the jaw of the salamander be cut off it is restored, 

 or if a part of the eye be removed it regenerates ; but if the en- 

 tire eye or the leg, " including the shoulder girdle," be removed, 

 neither is regenerated. A lizard can regenerate its tail, but not 

 its limbs, while most vertebrates can regenerate neither. 



If the tail of a fish be cut off near the base, it will be restored 

 to its original form, no matter whether the cut be square or 

 oblique. Not only that, but the rapidity of growth will not be 

 uniform at all points along the cut surface. The points at which 

 the growth will be most rapid depend upon two considerations, 

 the original form of the tail (whether bilobed or otherwise), 

 and the direction of the cut (whether square or oblique). It 

 will be more rapid at the points where most is to be restored 

 (see Fig. 35). 



On this point Morgan very pertinently remarks that " the 

 point of special interest is that the new material that appears 

 over the exposed edge does not first grow out at an equal rate 

 at all points until it reaches the level of the original fork (in a 

 bilobed tail), and then continue to grow in two regions, to form 

 the lobes of the tail," but the object is accomplished by differ- 

 ences in the rate of growth, and the " regions of most rapid 

 growth are very soon established in the new tail." 



Extensive experiments in regeneration among earthworms 

 have been conducted, not only by Trembley and Bonnet upon 

 Lumbriculus, but later by Morgan upon Allolobophora foetida? 



From these investigations it appears that : 



i . If in the last-named species one segment of the head be cut 

 off, it is promptly restored (see Fig. 36, B). 



1 Morgan, Regeneration, pp. 7, 8 ; also Fig. 35 of this book. 2 Ibid. pp. 3-10. 



