under which the present work was done made it practically impossible to carry out a thorough and complete investigation of the phototaxis of the embryos, so that in several particulars my results are incomplete. For this reason it seems preferable not to publish my observations in detail at this time. For the sake of indicating the general trend of the results as far as they go I will briefly summarize them. I was unable to get any evidence that the first reaction to light to appear after hatching was positive in sense. On the contrary it was clearly negative, regardless of whether the embryos were swimming or walking. Later there appeared a strongly marked positive reaction shown only by relatively few individuals. These individuals when responding in the positive sense to the direction of the incident light were, so far as my observations went, always swimming in a very violent manner. In the same dish at the same time, with all the embryos of approximately the same age, many individuals were negatively phototactic, fewer positively phototactic, and still fewer apparently indifferent to light. This applies to light of the intensity of diffuse sunlight. The negative phototaxis is apparently associated with a strong positive thigmotactic tendency. It seems very desirable that the reactions of Limulus to photic stimuli in any or all stages of its development be thoroughly investigated under proper conditions for experimentation. I know of no form which seems likely to give more interesting and significant results in this field than this organism. Discussion of Results. With the detailed results now in hand it is possible to make a direct comparison between the behavior of Limulus in its earliest larval stages and in the adult condition. In order make the comparison easy of comprehension the following table has been arranged. In parallel columns are stated the conditions with respect to certain definite features of the behavior in the two stages of the life history. Tabular Résumé of the Behavior of Limulus in the Earliest Stage of its Free Existence, and in the Adult. Respiratory Walking Movements. Righting Burrowing Essentially the same in character in embryo and adult. Definite, immedi ately purposive reaction. Probably same in embryo and adult. "Gill-scraping Complex and highly coördinated. Definite and pur poseful reflexes. Reflexes of Essentially the same in embryo and adult. Sixth Legs. Absent. "Cleaning" Movements of Gills. Present (cf. HYDE, loc. cit.) From this comparison it appears at once that, with a single exception, all the items of behavior presented by the adult are, in the case of the embryo, either entirely absent or present in essentially the same condition as in the adult. In other words, the embryo does not in general have simple types of be havior, which during development give way to more complex types leading up to the condition found in the adult. This seems to be a matter of some importance, for the reason that it indicates that it will be nearly or quite useless to look to larval stages for help in analyzing the adult behavior in forms like Limulus. It seems likely from what we know of the general correlation between type of behavior and general type of body form, that the same thing will be true in most cases where the general form relations of the body are closely similar in larval and adult stages. In Limulus this similarity in body form is very close, and the present paper shows how similar in essential features the behavior is in the two stages. The single exception to the general rule of essential similarity in type of behavior between adult and embryo in Limulus, is found in the swimming movement. In the embryo the legs take no active part in this movement, while in the adult they beat synchronously with the gills. So far as the legs are concerned we evidently have here a simpler type of behavior in the embryo than in the adult. The holding of the legs in a cramped position as described must be regarded as a definite action, just as any movement would be, only it is simpler in character than a rhythmical movement. The difference here in behavior between embryo and adult is without doubt associated with a morphological difference in the nervous mechanism. In the case of swimming and walking movements, and the righting reaction the study of the embryos give indubitable evidence that there is improvement with practice. The embryo performs these movements better-that is, with steadily increasing purposiveness-the more it practices them. At the time of hatching it is endowed, so to speak, with an ability to perform certain acts, but is unable to perform them in such a way that they serve any purpose at all well. The latter ability comes with practice. Shall we call this "learning through experience" how to do certain things? It seems to the writer that one who maintains that it should be so called will occupy . a practically impregnable position, yet he will be totally unable to prove that this necessarily involves any psychical element. On the other hand, the phenomena in a case like the one under discussion appear objectively analogous to certain phenomena in the inorganic world. For example: one gets a complicated piece of machinery fresh from the factory. If energy is put into it it will do certain things. But on account of the newness the parts do not work smoothly together. There is an undue amount of friction between the parts. As the machine is used the bearings get worn a little and we say that as a whole the machine "works better." The continued functioning improves the general coördination as a result of the interaction of the parts. Objectively very much the same sort of change appears to take place in the behavior of a Limulus embryo. Is there any more of a psychical element in the one case than in the other? This we obviously do not know, and it seems idle to discuss the question, since no amount of a priori reasoning will settle it and a posteriori evidence is not to be had. Literature Cited. Hyde, Ida H. '94. The Nervous Mechanism of the Respiratory Movements in Limulus polyphemus. Jour. Morph., IX, pp. 431-448, Pl. I-III, 1894. Kingsley, J. S. '85. Notes on the Embryology of Limulus. Q. J. Mur. Sci., N. S., XXV, pp. 521-576, Pl. XXXVII-XXXIX, 1885. '92. The Embryology of Limulus. Jour. Morph., VII, pp. 35-68, Pl. V-VI, 1892. Loeb, J. '93. Ueber künstliche Umwandlung positiv heliotropischer Thiere in negativ heliotropisch und umgekehrt. Arch. f. d. ges. Physiol., 54, pp. 81-107, 1893. Packard A. S., jr. '72. The Development of Limulus polyphemus. Mem. Boston Soe. Nat. Hist., II, pp. 155-202, Pl. II-V, 1872. |