The presence of a sense of smell in Star-fish was proved by keeping some of these animals for several days in a tank without food, and then presenting them with small pieces of shell-fish. The Star-fish immediately perceived the proximity of food, as shown by their immediately crawling towards it. Moreover, if a small piece of the food were held in a pair of forceps and gently withdrawn as the Star-fish approached it, the animal could be led about the floor of the tank in any direction, just as a hungry dog could be led about by continually withdrawing from his nose a piece of meat as he continually follows it up. This experiment, however, was only successful with Star-fish which had been kept fasting for several days; freshly caught Star-fish were not nearly so keen in their manifestations, and indeed in many cases did not notice the food at all.
Desiring to ascertain whether the sense of smell were localized in any particular organs, as we had found to be the case with the sense of sight, I first tried the effect of removing the five ocelli. This produced no difference in the result of the above experiment with hungry Star-fish, and therefore I next tried the effect of cutting off the tips of the rays. The Star-fish behaving as before, I then progressively truncated the rays, and thus eventually found that the olfactory sense was equally distributed throughout their length. The question, however, still remained whether it was equally distributed over both the upper and the lower surfaces. I therefore tried the effect of varnishing the upper surface. The Star-fish continued to find its food as before, which showed that the sense of smell was distributed along the lower surface. I could not try the converse experiment of varnishing this surface, because I should thereby have hindered the action of the ambulacral feet. But by another method I was able nearly as well to show that the upper surface does not participate in smelling. This method consisted in placing a piece of shell-fish upon the upper surface and allowing it to rest there. When this was done, the Star-fish made no attempt to remove the morsel of food by brushing it off with the tips of its rays, as is the habit of the animal when any irritating substance is applied to this surface. Therefore I conclude that the upper or dorsal surface of a Star-fish takes no part in ministering to the sense of smell, which by the experiment of varnishing this surface, and also by that of progressively truncating the rays, is proved to be distributed over the whole of the ventral or lower surface of the animal. For I must add that severed rays behave in all these respects like the entire organisms, although they are disconnected from the mouth and disc.