28 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
continually twisted around, making the process appear somewhat awkward. When in 
their tubes, however, the outer side of the tentacles would be most naturally used, and 
it is by their adherence to that side of the tentacles that particles of food and sand are 
brought to the mouth. This use of the outer side of the tentacles in locomotion was 
observed by Pourtales (’51) in the synapta from Florida, which he called 8. viridis. 
The New England synaptas seem to have organs of special sense of two kinds, 
olfactory and equilibratory or positional; no evidence of ability to distinguish between 
light and darkness could be detected and there are no anatomical structures to which 
this sense could be ascribed. The sense of smell is centralized in the cups on the 
inner side of the tentacles; that of position in the so-called “otocysts” or “auditory” 
organs. Semon (’87) has shown that 8. inhcerens possesses the sense of smell, and 
similar experiments made at Woods Hole confirm his results. If a piece of any rank- 
smelling substance is placed near the tentacles of a synapta they are immediately 
retracted and the head is turned away. Small bits of decayed starfish were used 
and it was found that the synaptas would avoid them even when they did not actually 
touch them, and they seemed to avoid sand with which decayed starfish had been 
mixed. While the experiments were not conclusive by themselves, they were satis- 
factory as confirmation of Semou’s work. 
In regard to the so called “otocysts” more numerous and more careful experiments 
were made, with results which seem to show conclusively that these organs are used 
to show the position of the animal in the water or sand. Semon (’87) has demonstrated 
the fact that synaptas appear to have no sense of sound and no ability to detect even 
strong vibrations in the water. He, however, left the function of these “otocysts” 
undetermined, but in a previous paper (Clark, ’98) I suggested that in S. vivipara 
they determined the animal’s position in the water. Experiments on inlmrens and 
roseola have fully confirmed this opinion and there can no longer be any doubt that 
this is their true function. In regard to their structure there is little to be added to 
Semon’s (’87) description, as it has not yet been possible to demonstrate the cilia which 
line them. That they are lined with cilia, which are in constant motion, can be easily 
seen in the living animal under the microscope. The siugle vesiculated cell or 
“otolith” which each “otocyst” contains may be seen to be constantly revolving and 
never actually rests against the wall of the sac, but is kept out from it, apparently, by 
these cilia. 
Cuenot (’91) in his description of these organs says that there are “un grande 
nombre d’otolithes spheriques” in eacli “otocyst,” and Semon (’87) says there are one 
or more (often six or more) “blaschen” in each sac. I have examined a large number 
of living specimens of both inhcerens and roseola aud I have never yet found a case 
where there was more than one. Whether these so-called otoliths are calcareous, as 
Cuenot thinks, or vesiculated cells filled with fluid, as Semon says, I have not been 
able to determine positively, though I incline to the latter view, as they do not appear 
calcareous when compared either by transmitted or reflected light with any undoubtedly 
calcareous body. But there can be no doubt that they are heavier than the fluid which 
surrounds them in the sac, as may be readily shown by the following simple experi- 
ment: If a pair of the sense organs are cut from a living synapta and placed under a 
cover-slip and examined under the microscope, the otolith will be seen in the center 
of the sac so long as the slide is perfectly horizontal. But if the microscope be tipped, 
so that the slide approaches a perpendicular position, the otolith will be seen to sink 
slowly to the lower side. (Owing to the reversal of upper and lower sides under the 
