Tabular Résumé of the Behavior of Limulus in the Earliest Stage of its Free Existence, and in the Adult.

Respiratory
Movements.
Swimming
Movements.

Walking

Movements.

Righting
Reaction.

Burrowing
Reactions.

Embryo.

Adult.

Same in character in embryo and adult.

Legs and gills both beat rhythmically and synchronously.

Gills only beat rhythmically.
Legs held in fixed position.
Gill movements the same in
character as in the adult.
Control of swimming move-
ment poor immediately after
hatching. Improve with prac-
tice.

Essentially the same in character in embryo and adult.
Not so well coördinated and directed in embryo as in
adult. Improve with practice in embryo.

Present from beginning but
not well coördinated. Not as
definite in type as in adult.

Definite,

immedi

ately purposive reaction.

Probably same in embryo and adult.

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 con cerned 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. Micr. 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.

Patten, W.

'93. On the Morphology and Physiology of the Brain and Sense Organs of Limulus. Q. J. Micr. Sci., N. S., XXXV, pp. 1-96, Pl. 1-5, 1893.

Pearl, R.

:03.

The Movements and Reactions of Fresh-water Planarians: A Study in Animal Behavior. Q. J. Micr. Sci., N. S., 46, pp. 509-714 1903.

EDITORIAL.

Since the days of GERLACH's reticulum there has been a growing tendency among neurologists of all schools to lay great stress on the functional importance of the neuropil, or feltwork of finest non-medullated nerve terminations. It would appear that here some of the most characteristic nervous reactions take place, and that the peripheral fibrillar networks are not less important. Just what these reactions are it is still too early to affirm with confidence, but the problem is being attacked from several sides and with a fair prospect of immediate success in some of its phases.

Anatomical interest centers now on neurofibrillae and enough facts have already been gathered in to justify the prediction that we shall not have to wait much longer for an accurate knowledge of what the structure of the neuropil really is. Physiological experimentation, too, is daily adding new facts and developing new points of view. Undoubtedly both of these classes of evidence must be greatly enlarged before we shall be in a position to determine just how far the newer conceptions of nervous function can be cast in the mold given by the terminology of the neurone as current in the decade just closed. Certain it is that we are not yet ready to throw away that terminology; for even a contracted and defective mold is better than none so long as it turns out fruitful hypotheses and promotes clear analysis and accurate expression, provided only one does not make a fetish of it and in the end perhaps come to venerate its very defects. Practically, even the most striking of our latest physiological experiments on the functional differentiation of the nervous elements can still be expressed more conveniently in terms of the neurone doctrine than in any other way.