THEORIES OF REGENERATION 263 



a certain extent, true. On the other hand, when we find that one of 

 the most complicated organs of the body, the eye, can regenerate in 

 the salamander, if only a piece of the optic cup is left attached to the 

 nerve, we may well doubt if there is any such direct and general con- 

 nection between regeneration and complexity as Weismann maintains. 



Weismann's so-called." mechanism " of qualitative nuclear division 

 is the basis of his conception of pre-formation. We are, I think, at 

 present in a position to reject not only this conception, since it finds 

 no support either in observation or experiment, but also his view that 

 regeneration is brought about by latent cells ; for it has been shown 

 in a large number of cases that the new cells come directly from the 

 old, differentiated ones. In a previous chapter it has been pointed 

 out that Weismann's idea that regeneration has been acquired by a 

 process of natural selection, and is under the influence of this sup- 

 posed agent, is in direct contradiction to a number of known facts. 

 Under these circumstances we are warranted, I think, in concluding 

 that the entire Weismannian point of view is wrong. 



The process of regeneration has been often compared to the pro- 

 cess by which a broken crystal completes itself. Herbert Spencer, in 

 particular, has elaborated this idea. In his book on the Principles of 

 Biology, he says : " What must we say of the ability an organism has 

 to recomplete itself when one of its parts is cut off ? Is it of the same 

 order as the ability of an injured crystal to recomplete itself? In 

 either case new matter is so deposited as to restore the original out- 

 line. And if, in the case of a crystal, we say that the whole aggregate 

 exerts over its parts a force which constrains the newly integrated mole- 

 cules to take a certain definite form, we seem obliged, in the case of 

 the organism, to assume an analogous force." Spencer has called 

 attention to a superficial resemblance between the renewal of a part 

 of a crystal and the regeneration of an animal, and without further 

 inquiry into the profound differences between the processes, assumes 

 that "analogous forces" are at work. Now that we know something 

 more of both processes, we find so much that is totally different, that 

 there remains no basis for Spencer's conclusion, namely, that analo- 

 gous forces must be present. Furthermore, Spencer's statement that 

 the whole crystal aggregate exerts over its parts a force of some kind 

 is diametrically opposed to our idea as to the method of "growth " of 

 a crystal in a saturated solution. The new material is added always 

 at the surface of the crystal, and the growth of each point is self-de- 

 termining. There is no central force that controls the deposition of 

 new material in the different regions. Rauber's work on the so-called 

 regeneration of the crystal has given us a clearer conception of how 

 the process is brought about. He has shown that when a piece is 

 broken from a crystal, and the crystal suspended in a saturated solu- 



