Ill] OF REGENERATIVE GROWTH 271 



Of regeneration, or growth and repair 



The phenomenon of regeneration, or the restoration of lost or 

 amputated parts, is a particular case of growth which deserves 

 separate consideration. It is a property manifested in a high 

 degree among invertebrates and many cold-blooded vertebrates, 

 diminishing as we ascend the scale, until it lessens down in the 

 warm-blooded animals to that vis smedicatrix which heals a wound. 

 Ever since the days of Aristotle, and still more since the experiments 

 of Trembley, Reaumur and Spallanzani in the eighteenth century, 

 physiologist and psychologist alike have recognised that the pheno- 

 menon is both perplexing and important. "Its discovery," said 

 Spallanzani, " was an immense addition to the riches of organic philo- 

 sophy, and an inexhaustible source of meditation for the philosopher." 

 The general phenomenon is amply treated of elsewhere*, and we 

 need only deal with it in its immediate relation to growth. 



Regeneration, like growth in other cases, proceeds with a velocity 

 which varies according to a definite law; the rate varies with the 

 time, and we may study it as velocity and as acceleration. Let us 

 take, as an instance, Miss M. L. Durbin's measurements of the rate 

 .of regeneration of tadpoles' tails : the rate being measured in terms 

 of length, or longitudinal increment f. From a number of tadpoles, 

 whose average length was in one experiment 34 mm., and in another 

 49 mm., about half the tail was cut off, and the average amounts 

 regenerated in successive periods are shewn as follows : 



Days 3 5 7 10 12 14 17 18 24 28 30 



Amount regenerated (mm.): 



First experiment 1-4 — 3-4 4-3 — 5-2 — 5-5 6-2 — 6o 



Second „ 0-9 2-2 3-7 5-2 60 6-4 7-1 — 7-6 8-2 8-4 



confidently done) that Smilodon perished on account of its gigantic tusks, that 

 Teleosaurus was handicapped by its exaggerated snout, or Stegosaurus weighed 

 down by its intolerable load of armour, we may call to mind kindred forms where 

 similar conditions did not lead to rapid extermination, or where extinction ensued 

 apart from any such apparent and visible disadvantages. Cf. F. A. Lucas, On 

 momentum in variation, Amer. Nat. xli, p. 46, 1907. 



* See Professor T. H. Morgan's Regeneration (316 pp.), 1901, for a full account 

 and copious bibliography. The early experiments on regeneration, by V^allisneri, 

 Dicquemare, Spallanzani, Reaumur, Trembley, Baster, Bonnet and others, are 

 epitomised by Haller, Elementa Physiologiae, viii, pp. 156 seq. 



t Journ. Exper. Zool. vii, p. 397, 1909. 



