A6 PROF. J. ARTHUR THOMSON ON 
Rauber calls an- imperfect embryonic stage; or a sphere of 
saltpetre will similarly regenerate a rhombic prism; and 
any mutilation of a crystal will be followed by a restoration 
of the normal form. I mean to hint that the gap between 
the little spherule of alum and the octahedral mass is 
comparable to the gap between the regenerative cap at 
the anterior end of a decapitated Naiad worm and the re- 
grown head. The gaps are bridged by a gradual series 
of differentiations and integrations. 
There is a second fact which we do well to remember in 
thinking about regeneration—the marvel of the process by 
which a decapitated earthworm or Planarian or Tubularian 
grows a new head, by which a curtailed earthworm or 
lizard grows a new tail, by which a newt grows a new lens 
or a new leg, so to speak, at command. This second fact 
is that we must try to allow for the influence of environing 
stimuli. The residual germinal power in the animal counts 
for much, but this is localised and operates under the 
influence of a particular environment, which also counts 
for much, though not for so much. 
Perhaps this point may be best understood by reference 
to what is called abstrusely heteromorphosis. A few 
illustrations must suffice. If a fragment be cut off a 
Tubularian, and one end be stuck in the sand, a head may 
regenerate at the free end whether that was originally 
upper or lower, oral or aboral. But if both ends be left 
free, the fragment regenerates a head at each end. Evidently 
the environmental influences count for something here. 
But while the common Zubularia can regrow its crown of 
tentacles at either end, the anemone Cerianthus can regrow 
them only at the distal end. So that not very far from the 
plastic Tubularia we find the less plastic Cerianthus, whose 
regenerative power is limited by something which we may 
call “inherent polarity "a something, at anyrate, which 
cannot be overthrown by altered external conditions, such as 
placing the piece upside down. Miss Bickford cut off the 
head of a Tubularian straight across, new tentacles were 
regrown at a certain distance from the wound; Driesch 
made the cut oblique, and the tentacles regrew obliquely 
to the longitudinal axis, and were not righted in the 
