Page:Popular Science Monthly Volume 75.djvu/144

140 trials it will regularly swallow the meat but usually discard the filter-paper. Thus it would appear that the sea-anemone had detected the deception practised on it in the beginning and had learned to circumvent the experimenter. But further observations show how erroneous this interpretation is. If the experiment just described is performed on a limited group of tentacles on one side of the oral disk and, after the animal has arrived at the stage of discriminating between meat and paper, the experiment is repeated on another and distant group of tentacles, it is found that these tentacles and the part of the mouth next them will accept both meat and paper as the first group did and the same process as was used on this group must be repeated on the second group in order to bring it to the stage of discrimination. Thus it is clear that, however we may regard these acts, Metridium shows no marked power of making the experience of one part of its body serve another; in other words, it shows no decided evidence of a central nervous organ.

This conclusion is in substantial accord with the recent results obtained by Fleure and Walton (1907) from experiments on Actinia except that they believe that the repeated trials on the tentacles of one side of the circle had in this form a slight influence on those of the other. This influence, however, was so slight that they declared that experience of this kind certainly did not become the possession of the animal as a whole.

Not only is there in these reactions absence of any strong evidence in favor of well-marked central nervous functions in anemones, but it is very doubtful if we are justified in regarding the local reaction just described as a true discrimination. Jennings (1905) has suggested that sea-anemones possess sensations of hunger and that as the experiment proceeds the animal's hunger diminishes and it finally discards when less hungry what it at first accepted. But Allabach (1905) has shown that the same so-called discrimination is arrived at if the sea-anemone is not allowed to swallow anything, but is robbed of meat and paper alike by having these materials picked out of its gullet just as they are about to be swallowed. In fact it seems quite clear that this process of apparent discrimination is in no sense due to centralized nervous functions, but is merely the result of exhaustion. At the beginning of each experiment the receptors are stimulated by the strong juices of the meat and the weaker juice of the paper. As they run down in efficiency, they come to a stage where they no longer react to the weaker stimulus of the paper and respond only to the meat. At this stage apparent discrimination takes place.

Not only do these experiments show no evidence of central nervous functions, but they indicate a decided looseness of nervous articulation. The activity of one side of the body of the sea-anemone has very little,