REG EN ERA TION. 1 8 7 



the body ; hence only a tail can develop, even at the anterior 

 end of the piece.^ 



In one passage Bonnet states that the fluids that flow towards 

 the head are there used up, and we must infer that these head- 

 nourishing fluids are being continually made somewhere else in 

 the body of the worm. It may be pointed out, in passing, that 

 this idea of Bonnet's, that the fluid passing towards the head 

 (he seems to have had the blood in view) is a special kind of 

 fluid laden with head-nourishing substances, is not in agree- 

 ment with what we know of the function of the blood or of 

 other fluids in the body. The tissues of the head may take 

 out of the blood those substances in it that they use in their 

 life processes, but the blood itself going to the head is not 

 specialized in a particular direction, and is the same fluid that 

 flows posteriorly in other vessels. 



Bonnet advanced three ideas : preformed germs ; head- and 

 tail-nourishing stuffs ; and the flow of these latter in definite 

 directions. I shall return later to these views and consider 

 them more fully. 



The process of regeneration has been often compared to the 

 completion of a broken crystal ; just as the growth of an animal 

 or of a plant is sometimes contrasted with the growth of a 

 crystal in a saturated solution. Herbert Spencer, in particular, 

 has elaborated this view. In his book on the Principles of 

 Biology^ he says : "What must we say of the ability an organ- 

 ism has to re-complete itself when one of its parts has been cut 

 off } Is it of the same order as the ability of an injured crystal 

 to re-complete itself .'' In either case new matter is so deposited 

 as to restore the original outline. And if in the case of the 

 crystal we say that the whole aggregate exerts over its parts 

 a force which constrains the newly integrated molecules to 

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

 the organism to assume an analogous force." Starting here 

 with an hypothesis that is no longer held, viz., "that the whole 



1 Bonnet does not tell us how, in this case, the germs are awakened, since tail- 

 stimulating fluids are assumed to flow backwards. Perhaps, only tail germs being 

 present, he did not think it necessary to apply his subsidiary hypothesis. 



'^ Chapter IV, Waste and Repair. First published in 1863. I quote from the 

 last edition, 1S98. 



