316 CAUSES OF VARIATION 



influence. Heat, chemical action, light, electricity, all are in- 

 fluences that penetrate to the very constitution of the proto- 

 plasm, even of the germ perhaps. The most significant biological 

 fact in these studies is the wide range of adaptation and the 

 exceedingly diverse conditions under which living matter may 

 continue to discharge its normal functions, either unaltered or 

 but slightly modified, and the next most significant fact is the 

 more or less permanent alteration in functional activity through 

 changed conditions of the order mentioned. 1 



SECTION VII EVIDENCE FROM REGENERATION 



All animals and plants have more or less power to restore lost 

 or injured parts. It is noticeable, and perhaps significant, that 

 the power of regeneration is, roughly speaking, in inverse ratio 

 to the degree of differentiation ; that is to say, lower organisms 

 have, in many cases at least, almost unlimited powers of regenera- 

 tion, while among the highest species the ability to restore lost 

 parts is very slight. 



The bearing of this matter upon the question in hand the 

 relative stability or instability of living matter is of course not 

 in \h&fact of regeneration but in the character of the regenerated 

 part as compared with the original, and in the general behavior 

 of the organism when occasion for regeneration arises. Most of 

 the instances given in this connection are drawn from Morgan's 

 excellent work, Regeneration. 



Regeneration in animals. 2 Trembley (1740), Reaumur (1742), 

 Bonnet (1745), and Spallanzani (1768) were early investigators 

 in this subject. Their experiments have been often repeated and 

 their observations extended until the field has been well worked 

 and the limits of regeneration fairly well established. 



If the foot of a salamander be cut off a new one regenerates. If 

 the entire leg be removed it regenerates, and at whatever point the 



1 For additional references on acclimatization see Darwin's Origin of Spe- 

 cies, and his Animals and Plants under Domestication, II, 295-305 ; Vernon, 

 Variation in Animals and Plants, pp. 379-387 ; Bailey, Survival of the Unlike 

 (second edition), pp. 307, 310, 320 ; Weismann, Studies in the Theory of Descent, 

 pp. 555-622 ; Morgan, Evolution and Adaptation, pp. 319-325. 



2 Morgan, Regeneration, pp. i-io. 



