ZOOLOGY: P. H. COBB 
235 
forth some curling but almost no buckling. Currents of water when driven 
against the palp have very little effect as stimuli unless they are strong enough 
to indent the palp. 
The palps are also open to chemical stimulation and the responses thus 
called forth are commonly much more pronounced than those due to 
mechanical stimulation. The chemical stimuli employed consisted in solu- 
tions of a number of common salts, acids, and alkalis, of such non-electrolytes 
as ethyl alcohol, sugar, urea, quinine and so forth, and of mixtures such as 
beef extract and the like. These were used in varying concentrations and to 
all, except sugar, a reaction much like that seen in vigorous mechanical stimu- 
lation was observed. In reaction to chemical stimulation, however, the palp 
showed a tendency to roll up tightly from the tip rather than simply to curl 
upon itself. 
Electricity is also a stimulus for the palp. A faradic current just strong 
enough to be slightly stinging to the human tongue caused the palp to respond 
as to a mechanical stimulus. In efficiency the electrical stimulus was appar- 
ently midway between the mechanical and the chemical stimuli. 
A jet of hot water that emerged from the container at 54°C. caused the palp 
to curl vigorously when it was directed on that organ in water at 16.5°C. 
A similar jet of water at the temperature of that in which the clam was, had no 
stimulating effect on the palp. 
A beam of sunlight, or of strong electric light, or a sudden burst of light from 
flash-light powder had the remarkable property of causing the palp to curL 
The response, which of course occurred well under water, though slower in. 
its appearance than the responses to other forms of stimuli, followed so quickly 
on the stimulus that there was no doubt that the light, and not some accom- 
panying disturbance, was the effective agency. 
The surprising feature in all these responses is that they take place as ef- 
fectively on a palp that has been freshly cut from a clam as on the palp intact.. 
Careful comparative inspection of the reacting palps disclosed no obvious dif- 
ference between the efficiency of these organs when normally attached to the 
clam and after they had been severed from it. On cutting a palp from a clam 
for experimental work, it is well to allow it to remain at least a quarter of an 
hour in quiet water before subjecting it to stimulation. Such a palp is re- 
sponsive for about an hour and a half after removal. This condition shows 
that the palp contains within itself the neuromuscular organization necessary 
for all the responses described in this paper, and that it, therefore, possesses an 
autonomy even more complete than that of the vertebrate heart and compara- 
ble with what is shown by the tentacle of an actinian. 
It is intended to continue the line of investigations suggested by these 
studies and to extend them to the histology of the parts concerned. 
1 Contributions from the Zoological Laboratory of the Museum of Comparative Zoology- 
at Harvard College. No. 311. 
