August 16, 1901.] 



SCIENCE. 



237 



less the power of regenerating the lost organ 

 existed, or was acquired at the same time 

 as the extreme sensitiveness that brings 

 about the reaction. Lang does not state, 

 however, explicitly that he believes the re- 

 generative power to have arisen through the 

 exposure of the tail of the lizard and the 

 tail of the snail to injury, although he 

 thinks that the mechanism by means of 

 which these parts are thrown off has been 

 acquired in this way . Several other writers 

 have, however, used these same cases to il- 

 lustrate the supposed principle of liability 

 to injury and power of regeneration. 



Weismann in his book on ' The Grcrm 

 Plasm ' has adopted the principle of a con- 

 nection between regeneration and liability 

 to injury and has carried it much further 

 than have other writers. We can, there- 

 fore, most profitably make a careful ex- 

 amination of Weismann's position. His 

 general idea may be gathered from the fol- 

 lowing quotation:* "The dissimilarity, 

 moreover, as regards the power of regener- 

 ation i7i various members of the same species, 

 also indicates that adaptation is an im- 

 portant factor in the process. In proteus 

 which in other respects possesses so slight 

 a capacity for regeneration, the gills grow 

 again rapidly when they have been cut off. 

 In lizards again this power is confined to 

 the tail, and the limbs cannot become re- 

 stored. In these animals, however, the tail 

 is obviously far more likely to become muti- 

 lated than are the limbs, which, as a matter 

 of fact, are seldom lost, although indi- 

 viduals with stumps of legs are occasionally 

 met with. The physiological importance 

 of the tail of a lizard consists in the fact 

 that it preserves the animal from total de- 

 struction, for pursuers will generally aim 

 at the long trailing tail,t and thus the ani- 



* ' The Germ-Plasm.' Translation by W. Newton 

 Parker, 1893, page 116. 



t There are no facts that show that this statement is 

 not entirely imaginary. T. H. M. 



mal often escapes, as the tail breaks off 

 when it is firmly seized. It is, in fact, as 

 Leydig was the first to point out, specially 

 adapted for breaking off, the bodies of the 

 caudal vertebrae from the seventh onward 

 being provided with a special plane of 

 fracture so that they easily break into two 

 transversely. Now if this capability of 

 fracture is provided for by a special arrange- 

 ment and modification of the parts of the 

 tail, we shall not be making too daring an 

 inference if we regard the regenerative 

 power of the tail as a special adaptation, 'pro- 

 duced by selection, of this particular part of the 

 body, the frequent loss of which is in a certain 

 measure provided for, and not as the outcome 

 of an unknown ' regenerative power ' pos- 

 sessed by the entire animal. This arrange- 

 ment would not have been provided if 

 the part had been of no, or only of slight, 

 physiological importance, as is the case in 

 snakes and chelonians, although these ani- 

 mals are as highly organized as lizards. 

 The reason that the limbs of lizards are not 

 replaced is, I believe, due to the fact that 

 these animals are seldom seized by the leg, 

 owing to their extremelj^ rapid movements. " 

 Overlooking the numerous cases of the re- 

 generation of internal organs that have 

 been known for several years, and basing 

 his conclusion on a small, unconvincing ex- 

 periment of his own on the lungs of a few 

 salamanders, Weismann concludes : "Hence 

 there is no such thing as a general power 

 of regeneration ; in each kind of animal 

 this power is graduated according to the 

 need of regeneration in the part under con- 

 sideration ; that is to say, the degree in 

 which it is present is mainly in proportion 

 to the liability of the part to injury." 



After arriving at this conclusion the fol- 

 lowing admission is a decided anticlimax : 

 " The question, however, arises as to 

 whether the capacity of each part for re- 

 generation results from special process of 

 adaptation, or whether regeneration occurs 



