390 J. M. D. OLMSTED 
CONCLUSION 
Throughout all these experiments the influence of the nerve 
is most marked. On one hand, the degeneration of the nerve 
leads to the disappearance of the taste buds and is the cause 
of the failure of the barbel to regenerate, and on the other, 
regeneration of the nerve is accompanied by reappearance of the 
taste buds, and the presence of a normal nerve insures perfect 
regeneration. 
To account for all these facts one may assume that there is 
given off by the nerves a chemical substance of the nature of a 
hormone, which is necessary to the existence of the taste cells 
and also for regeneration. One hesitates to impose another 
burden upon this already too heavily laden theory, but it accounts 
for all the phenomena as no other does. If there is given out by 
healthy normal nerves some definite chemical substance which 
is necessary for the existence of the taste cells and for regener- 
ation, then, with a degeneration of the nerve and the lack of 
this substance, the taste cells must die and regeneration 1s impos- 
sible. Because in cold-blooded animals degeneration of the nerve 
is delayed for some time, the nerve is still able to send forth this 
substance, though connection with the central nervous system 
may have been lost. Morgulis (12), after a critical survey of 
the literature and comparison with the results of his own experi- 
ments on ophiurans, came to the conclusion that the influence 
of the nervous system on regeneration is paramount. Presence 
of the nerve at the wound surface, according to his view is a 
conditio sine qua non for complete regeneration. It will be seen 
that regeneration in the barbels of Amiurus obeys this rule 
perfectly. Goldfarb (’09) found that in the earthworm and in 
a certain marine annelid as well (’14), complete heads would 
regenerate even though there might be no connection whatever 
between the new heads and the old nervous system. Hunt (719) 
found that absence of the digestive tube did not check regen- 
eration, but when both digestive tube and nerve were removed, 
he never found head structures regenerated before the nerve 
cord and digestive tube had grown forward toward the anterior 
