KEGENERATION 19 



a principle which always creates what is useful. I refer to the 

 regeneration of the lens in the newt's larva. 



G. Wolff, an obstinate opponent of the theory of selection, 

 attempted to solve the same problem as I had before me in my 

 experiments on the regeneration of the internal organs of newts, that 

 is, he tried to answer the question whether organs which are never 

 exposed to injury or to complete removal in the conditions of natural 

 life, and which could not therefore have been influenced in this 

 direction by the processes of selection, are nevertheless capable of 

 regeneration. He extirpated the lens from the eye of Triton larvas, 

 and saw that in a short time it was formed anew, and from this he 

 concluded that there was here ' a new adaptiveness appearing for the 

 first time,' and that therefore adaptive forces must be dominant within 

 the organism. The current theory of the ' mechanical ' origin of 

 vital adjustments seemed to some to be shaken by this, and the 

 proclamation of the old ' vital force ' seemed imminent. And in 

 truth, if the body were really able to replace, after artificial injury, 

 parts which are never liable to injury in natural conditions, and to 

 do so in a most beautiful and appropriate manner, then there would 

 be nothing for it but at least to regard the faculty of regeneration as 

 a primary power of living creatures, and to think of the organism as 

 like a crystal, which invariably completes itself if it be damaged 

 in any part. But we have to ask whether this is really the case. 



What makes the regeneration of the lens seem particularly sur- 

 prising is the fact that in the fully formed animal it must arise in 

 a manner different from that in which it develops in the embryo, that 

 is, it must be formed from different cell-material. In the embryo it 

 arises by the proliferation and invagination of the epidermic layer of 

 cells to meet the so-called ' primary ' optic vesicle growing out from 

 the brain — a mode of development which cannot of course be repeated 

 under the altered conditions in the fully developed animal. The 

 reconstruction of the organ must therefore take place in a different 

 way, and if the organism were really able, the very first time the lens 

 was removed, to react in a manner so perfectly adapted to the end, 

 and so to inspire certain cells, which had till then had a different 

 function, that they could put together a lens of flawless beauty and 

 transparency, we should have reason to suspect that nearly all our 

 previous conceptions were erroneous, and to fall back upon a belief in 

 a spiritus rector in the organism. 



But the excision of the lens in these experiments was not by any 

 means an unprecedented occurrence ! It is true enough that newts in 

 their pools are not liable to an operation for cataract, but it does not 



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