48 PROF. J. ARTHUR THOMSON ON 
My second instance is more clear cut. Calucci, Wolff, 
and Miiller have made the experiment of extracting the 
lens of Triton, with the result that it was normally 
regenerated. From what, however? Not from remaining 
debris of the lens, for there was none, but from the iris, 
Leucocytes at the edge of the iris begin to take off pigment 
from the posterior layer, the cleared iris cells proliferate, 
the mass formed becomes a saccule, and the posterior wall 
of this saccule forms the characteristic crystalline fibres of a 
new lens. Now, since the lens-is normally formed from 
the ectoderm in front of the optic cup, and has no genetic 
connection with the iris, it is startling to find that the iris 
should regenerate it. If the facts be all right, and we have 
at least three observers, this case seems against the theory 
that specific regeneration-germs reside in particular areas. 
We might expect the iris to have iris-regeneration-germs, 
but it seems able to remake a lens, in whose original making 
it plays no part. So far as I can see, the case favours the 
view that the residual germinal power localised here and 
there in animals is more general and less specific than some 
suppose. It may be noted further that the newt is an 
animal with great regenerative power in many parts, and 
may be contrasted with an animal like the rabbit, where 
regeneration of the lens does not follow after complete 
extirpation, but only if some portion be left (Gonin). 
Moreover, it must be remembered that the posterior 
epithelium of the iris, which regenerates the lens, is. 
ectodermic. 
In conclusion, let me say again that the times do not 
seem to be ripe for a theory of the actual mechanism of 
regeneration. I should only weary you if I tried to make 
clear the provisional theory of Weismann and the criticisms: 
of it by men like Professor Morgan. 
A crocodile loses a tooth, but beneath its hollow base 
there is another ready to fill the gap, and not far off there 
is the rudiment of another. The adder casts a fang; behind 
it there is another ready to slip into place, and to re-- 
establish in a most interesting way a connection with the 
poison duct. Now, we may suppose that when a crab loses a 
claw there is resident at the area of rupture a rudiment 
