NOVEMBER 5, 1897. ] 
posteriorly does not depend, directly, on the 
size of the piece. 2. Anterior ends contain- 
ing from thirteen (?) to thirty segments 
sometimes regenerate posteriorly, but only 
after a long time and in general, the shorter 
the piece (i. ¢., the nearer the cut to the 
anterior end) the longer the interval before 
it begins to regenerate, and the fewer the 
pieces that regenerate at all. 3. Similarly 
very short posterior pieces do not regener- 
ate anteriorly; longer pieces from the poste- 
rior end regenerate occasionally, but only 
after a long interval of time. In general 
the shorter the posterior piece the longer 
the time before the piece begins to regener- 
ate anteriorly. 4. The experiments show 
that Weismann’s hypothesis of latent cells 
is insufficient to explain the phenomena of 
regeneration, because it can not account for 
the delay in regeneration of a lost part 
under the circumstances given above. 5. 
Short pieces from the middle of the worm 
sometimes regenerate both anteriorly and 
posteriorly. 6. If a worm be cut in two 
pieces and then the anterior end be cut off 
again from the anterior piece, the middle 
piece will regenerate posteriorly at the same 
rate and time as though the anterior end 
had not been cut off. 7. If posterior ends 
of two worms be sewed together and if then 
one of the ends has a part cut off, the part 
that regenerates is like the part removed ; 
i. e., @ new posterior end, and not a new 
head regenerates. 
The power to regenerate is, in Some cases, 
of the greatest use to an animal since it en- 
ables the animal, if injured, to reproduce 
the lost parts. It is, therefore, surprising 
to find the phenomenon of regeneration 
almost entirely neglected by the advocates 
of the theory of natural selection. Darwin 
searcely alludes to the matter and most of 
his followers make little or no reference to 
the subject. Weismann, however, in his 
recent book on the Germ Plasm has opened 
up the question. A quotation will serve to 
SCLENCE. 
693 
show how successfully he has treated the 
matter from the selectionists’ standpoint. 
“The power of regeneration in any particular 
part cannot depend only on the conditions 
which exist as regards the species under 
consideration ; it must also be due to ar- 
rangements for regeneration which have 
been transmitted by the ancestors of the 
species. Leaving the question aside, and 
regarding the power of regeneration as 
merely depending in each individual case 
on adaptation, we should arrive at some 
such conclusion as the following: the pro- 
vision of the cells of a certain part with 
supplementary determinants for the pur- 
poses of regeneration depends primarily 
on the liability of this part to frequent 
injury * * * * a useless or almost 
useless rudimentary part may often be in- 
jured or torn off without causing processes 
of selection to occur which would pro- 
duce in it a capacity for regeneration.” 
How an infinite number of injuries to a part 
could ever produce in it a capacity for regen- 
eration is far from clear. Injured animals 
would be, on the whole, at a disadvantage 
in the struggle for existence; if some of 
them have the power to regenerate already 
they are neither better nor worse off than 
those that have not been injured. Just 
how injured animals would ever be able in 
each generation to obtain an advantage 
Over uninjured animals is by no means self- 
evident. In my experiments, for instance, 
I find that only rarely do posterior ends of 
worms cut in the middle regenerate ante- 
riorly, and even in those cases where this 
happens the regeneration is almost always 
imperfect. Does this mean that as yet an 
insufficient number of these worms have 
been injured in this way? In the course 
of time if more worms are injured by acci- 
dents, will Allolobophora foetida acquire a 
capacity for regenerating the anterior end ? 
Are we to consider seriously this interpre- 
tation of the selection theory ? 
