THE WONDER OF LIFE 557 



in mind in connection with the re-growth of lost parts. 



Fourthly, it may be profitable to keep by themselves 

 those cases where an artificially excised small fragment 

 is able in favourable conditions to re-grow an entire organ- 

 ism. A fragment of a Uverwort thallus wiU re-grow the 

 whole plant, a piece of Begonia leaf will develop into a 

 complete plant with root and stem and flower, a corner of 

 potato-tuber with an " eye " has the same capacity — so 

 f amihar that it has ceased to excite our wonder. A piece of 

 Sponge may be cut off and ' bedded out ' ; a Hydra may 

 be cut into many parts each viable ; one Planarian worm, 

 haK an inch long, may give rise to a dozen worms if cut 

 into a dozen pieces. 



Julian S. Huxley has confirmed H. V. Wilson's observa- 

 tions on the remarkable behaviour of cells strained off 

 from chopped-up sponge. He worked with a common 

 vase-Uke calcareous sponge, Sycon rafhanus, and found 

 that some of the cells moved like amcebee and united into 

 small confused clumps of irregular size — a process quite 

 unhke anything that occurs in the ordinary Ufe of sponges. 

 Then followed processes of re-organization and re-develop- 

 ment, in some respects hke those of normal embryonic 

 development. Two layers of cells were estabhshed, 

 spicules were formed, a gastral cavity and an exhalent 

 aperture appeared, and one of the ' regenerates ' hved 

 and grew as a functioning sponge for several weeks. This 

 illustrates what we venture to call the indomitable virihty 

 of hfe. 



We see, then, in approaching the problem of the regenera- 

 tion of lost parts — say, hzard's tails, newt's legs, snails' 

 horns, starfishes' arms — that it is useful to bear in mind 

 some cognate phenomena : — (1) some of the facts of 



