JUNE 28, 1901.] 
periment several times with a similar result. 
Thinking that the failure to regenerate a head 
might be due to the presence of the pharyngeal 
pouch, I then cut fourteen specimens trans- 
versely behind the pharynx. Two days after 
the operation an interesting difference in the 
reactions of the anterior and posterior parts 
was noticeable. While the former reacted in 
all respects like normal individuals, the latter 
showed no definite reactions of any sort but re- 
mained scattered over the bottom, some with the 
ventral surface up. In six days all the pos- 
terior pieces were dead without having shown 
any signs of regeneration, while all the an- 
terior pieces, kept in the same dish, were liv- 
ing and regenerating new tails. This experi- 
ment was afterwards repeated with similar re- 
sults, and I soon became convinced that, in 
this form, while a tail might regenerate at any 
place from the pharynx back, a new head 
could not be formed in this region of the 
body. 
‘The question was now, could a new head 
be regenerated in front of the pharynx? So 
specimens were cut in two immediately in 
front of the pharynx. The result of these ex- 
periments was that, while a very narrow bor- 
der of new tissue might be formed at the cut 
border of the posterior piece, there was never 
any regeneration of even the semblance of a 
head. The anterior pieces, on the other hand, 
regenerated a new tail as before, and also a 
new pharynx. 
‘‘In the next experiment the heads of five 
individuals were removed by a transverse cut 
just behind the eyes. 
generate, but in five days it was apparent that 
the decapitated pieces were regenerating new 
heads ; in one piece the eyes could already be 
seen. On the next day eyes had appeared in 
all. The capacity for regeneration of a head 
was thus demonstrated. 
“Two questions now remained: Was the 
regeneration of a new head due to the size of 
the piece, or to the position of the cut? and 
how far back does the capacity for regeneration 
of a head extend? The first question received 
a very simple answer; the head was first cut 
off just back of the eyes, and then from the an- 
terior end of the major piece asmall transverse 
SCIENCE. 
The heads did not re- 
1027 
piece wascut. In six days a rudimentary head 
with eyes developed on the front end of the 
small piece in one of three specimens. 
‘“ How far back does the capacity for regenera- 
tion of a head extend? We have seen that it 
cannot be formed from tissue just in front of the 
pharynx, but that it can be formed just back 
of the eyes. Twelve specimens were cut trans- 
versely about half way between the front end 
of the pharynx and the anterior end of the 
body. The reactions of both parts were per- 
fectly normal, though the headless parts re- 
acted much less rapidly than the parts with 
heads. In seven days both parts were rapidly 
regenerating and eyes had appeared in the 
headless parts ; in the head-bearing parts the 
new pharynx was regenerating in the new tail. 
Both kinds of parts then completed the regen- 
eration rapidly, though even after nineteen 
days the normal proportions were not re- 
stored. 
“Thus in Dendrocelum new tissue may 
grow out in the form of a tail at any transverse 
level of the body, excepting only the most 
anterior part to a very short distance back of 
the eyes; the capacity for regeneration of a 
head, however, is limited to the anterior third 
or fourth of the body. Ido not mean to assert 
that the formation of a new head back of this 
level is completely impossible. Some one may 
at any time demonstrate, by taking suitable 
precautions, that a new head may be formed 
back of this level. But it is shown very clearly 
by these experiments that the power of regen- 
erating a new head is largely, if not entirely, 
confined to the prepharyngeal part of the body 
in Dendrocelum, and that-it is always greater 
at any more anterior transverse level. 
“Thus it is demonstrated that in Dendroce- 
lum. (1) The power of regenerating a head is 
limited to a small part of the body. (2) Thata 
new tail may be generated at any transverse 
level. (3) That the capacity for remolding de- 
generating parts into normal proportions is. 
very limited. (Limitation of ‘morpholaxis,’ 
Morgan.) (4) That there is a relation between 
the power of regeneration in this form and the 
power of performing the usual coordinated 
movements, the latter power always being 
slight in parts incapable of regeneration. This. 
