REGENERATION OF LOST PARTS IN ANIMALS. 45. 
normal after repeated moultings (Zool. Anzeig., xix. (1896), 
pp. 424-5. 2 figs.) He also makes the note, which others. 
confirm, that young animals regenerate lost parts more 
rapidly than older forms do. Just as some plants show a 
reduction of cambium as they grow older, so there may be 
a reduction in the residual germ-stuff which in some way or 
other is instrumental in effecting regeneration. 
In thinking about regeneration the marvel of the 
process by which the stump of a snail’s horn will regrow 
the whole horn with the eye at the tip included, and will 
regrow it not once or twice, but as often apparently as the 
experimenter’s patience lasts—we should, I think, recall two- 
important biological ideas. The first is the way in which 
one stage in growth gives rise to another. Between 
the apparently simple egg and the obviously complex bird 
there seems such a gap, that we are bewildered by the 
apparent disproportion between cause and effect. But the 
bewilderment lessens as we follow the development from. 
stage to stage, and see how one phase naturally and gradually 
leads on to the next. The words gradual differentiation 
and integration solve no mystery, but they save us from a 
false perspective. And what is true of embryonic develop- 
ment is to some extent true also of regenerative growth. 
It is, of course, striking to see how from within its. 
cuticular sheath there suddenly bursts forth a beautifully 
formed lobster limb, stretching itself out like a Jack-in-the- 
box. But the abruptness of the phenomenon is wholly 
superficial; there has been a long period of gradual 
differentiation within the husk of the limb-bud. There 
are not many Jack-in-the-box phenomena in organic nature. 
I do not see my way at present to any theory of the 
mechanism of regeneration, nor do I believe that the 
times are ripe for it. But it is well to point out that we 
must not make the miracle more mysterious than it is. 
Comparisons between living creatures and crystals are apt. 
to be misleading, though their utility will perhaps be 
recognised in the future; but let me remind you that a 
minute fragment of alum, fashioned artificially into a sphere, 
or a cylinder, or a lens, will, when dropped into a solution. 
of alum, develop into a perfect octahedron, through what. 
