Page images

cult of accomplishment. For some time before the present piece of work was begun it was the opinion of the writer that valuable aid in the analysis of the behavior of higher organisms might be gained by following the plan of the morphologist and studying the developinent in the individual of the characteristic features of the behavior. Just as the morphologist studies the ontogeny of an organ as an aid to the understanding of the adult condition, so might the comparative psychologist study the ontogeny of a reaction. It seemed reasonable to suppose, in view of the close relationship which JENNINGS and others have shown to exist between structure and type of behavior in lower forms, that in higher forms the behavior would be simpler in character during embryonic or larval life when the structure is simpler. Of course we know in a general way that this is true; but does it hold in detail for single complex reactions and reflexes ? So far as is known to the writer, very little systematic work on behavior has been done from this point of view, except on some of the mammals and birds (cf. notably the work of Mills, LLOYD MORGAN and SMALL). In these forms the behavior has evidently a considerable psychical element in it. It was with the idea of determining whether anything of importance might be gained by studying the ontogeny of reactions primarily reflex in nature that the present piece of work was undertaken.

The form chosen for study was the king-crab Limulus polyphemus. The reasons for this choice were two fold; in the first place, I was already familiar with the behavior and reactions of the adult organism, and in the second place, Limulus is a form in which the behavior is quite complex, and yet at the same time the different reflexes are strikingly definite and machine-like in character. The adult Limulus is an almost ideal form for physiological work, on account of its tenacity to life after most extensive operations have been performed upon it, and because of the definiteness of its responses. Something of the complexity as well as the definiteness of its behavior can be gathered from the excellent account which PATTEN ('93) has given of the gustatory reflexes, for example.

The behavior of the adult Limulus is principally made up of the following movements and reflexes: the respiratory movements of the abdominal appendages, the swimming movements of the abdominal and thoracic appendages, various “gill cleaning" reflexes of the abdominal appendages and the sixth legs, walking movements, and the reflexes of gustation and deglutition. Furthermore, it responds to temperature stimuli very strongly and characteristically, also to certain sorts of tactile stimuli, to disturbances of its equilibrium, to chemical stimuli, and is thigmotactic and phototactic. The original plan of the present work was to make a thorough detailed study of the behavior and reactions during every stage of development from the time the embryo left the egg membranes till it attained the adult condition, in its behavior at least. It was hoped that in this way steps in the development of the reactions and reflexes could be traced.

The work was begun in the U. S. Fish Commission Laboratory at Wood's Hole, in July, 1900, and continued throughout the summer. In that time the behavior was studied and the work finished from my point of view (with the exception of the phototactic reaction) up to the stage at which the first moult occurs (end of the so-called "trilobite" stage). During the following fall a preliminary statement of the results obtained was published in Science.1 It was expected at that time that the work would be taken up again the next summer and older stages studied.

This, however, proved to be impossible and at no time since have I been able to take up the work again. As it is uncertain when I shall be able to go on with this problem it has seemed desirable to publish the results so far obtained. I wish to put on record the complete statement of the facts made out in the two developmental stages which have so far been investigated.

It gives me pleasure to make acknowledgement at this point to those who have in one way or another aided in this work. To Professor WM. PATTEN, my friend and former

IN. S. Vol. XII, No. 311, pp. 927-928, 1900.

teacher, I am indebted, not only for the material on which the work was done, which he very kindly furnished me, but also for many helpful suggestions freely offered as the work progressed. When the work on Limulus embryos was begun I had already been engaged for two years on a study of the physiology of the brain of the adult animal, under his direction. Without the thorough knowledge of the adult behavior thus gained the present study would hardly have been possible. To the authorities of the U. S. Fish Commission, and especially to Dr H. C. BUMPUS, I am indebted for the numerous facilities which were freely placed at my disposal at the Wood's Hole Laboratory.

Material and Methods.

The material used consisted of several hundred developing Limulus eggs which were given me by Dr. PATTEN. When received they were nearly all at about the stage of development, designated as Stage I, by KINGSLEY ('92). At room temperature development proceeds quite rapidly, but owing to the fact that there is a great deal of variation in the rate of development, individuals in widely different stages of development may be found at any time in the same batch of eggs. The eggs and embryos were kept in shallow glass dishes in sea-water which was changed at intervals, usually once in twenty-four hours. In this way the embryos were kept in good condition for a period of nearly two months.

The results of the present work will be discussed under two headings: first the behavior and reactions before the embryo leaves the egg membrane (“'vicarious chorion," KINGSLEY's Stage I), and second, the behavior up to the time of the first moult after the animal begins its free existence (the so-called "trilobite” stage, KINGSLEY's Stage K). General accounts with figures of the morphological development of Limulus are given by KINGSLEY ('85 and '92).

The Bohavior before the Embryo begins its Froe Exlatence.

Stage of Development.—The earliest stage at which definite results could be obtained regarding the movements and reac

[ocr errors]

tions of the Limulus embryos was shortly before the time of hatching. At this stage the embryo has a distinctly limuloid appearance in nearly all respects. Ail the appendages are formed, and are movable, with the exception of the long telson characteristic of the animal in later stages. The legs are formed on the same plan as those of the adult female, the secondary sexual modifications of the chelae of the first pair of walking legs in the male, not yet appearing. In this and the succeeding stages the embryos have a general, superficial resemblance to a trilobite which has led to the designation of these as the “'trilobite stages" in the development The embryo lies in the “vicarious chorion" (cf. PACKARD '72, and KINGSLEY, '85, p. 525) surrounded by fluid. The "vicarious chorion" is considerably greater in diameter than any dimension of the embryo, so that there is considerable free space on all sides of the latter. The embryo at this stage is about 4 mm. in length. The following account of the behavior within the vicarious chorion" applies to embryos at any time within a week before hatching. Closer time relations than this, as will appear from the account, cannot be fixed in the development of the reactions of this organism.

Normal Position of the Embryo. —The embryo lies at the bottom of the hollow sphere formed by the vicarious chorion," with its neural side uppermost. This position is simply the result of the action of gravitation, the embryo sinking to the

, bottom of the sphere because of the fact that its specific gravity is greater than that of the surrounding fluid. The reason for its lying with the neural surface uppermost is to be found in the fact (to be brought out in detail in another connection) that it is unable, under the circumstances in which it finds itself, to get into and retain any other position in which it is in stable equilibrium.

Movements within the Vicarious Chorion."-In the descrip

' I shall speak of the developing organisms throughout as "embryos.” The rupturing of the “vicarious chorion” and beginning of free larval life, will be termed the “hatching." These expressions are used merely for verbal convenience.


tion of the movements of the embryo within the “vicarious chorion" the abdominal appendages will be considered first, as the phenomena here are relatively simple in character.

The abdominal appendages (operculum and gills) begin characteristic, rhythmical respiratory movements at least five days before hatching. It is probable that in reality such movements begin even earlier than this, but I have no observations going farther back. The ordinary respiratory movements when first observed are precisely like the same movements in the adult Limulus. They consist of a rhythmical, up-and-down beating of the gills, each gill book being opened during the phase of expansion, or “inspiratory” phase, to adopt the terminology of Miss HYDE ('94).

There is, however, one significant difference in the respiratory movements of embryos and adults. This is in the

In the adult the normal rate is about twenty-five to thirty beats per minute. In the embryos the rate is markedly more rapid, the average number of beats from my observations being sixty per minute. The range of variation is from 55 to 60 beats per minute. The rhythm of the beats is quite as perfect in the embryos as in the adults.

These respiratory movements are the only movements which the abdominal appendages perform before the embryo leaves the "vicarious chorion,” so far as I have observed. I was never able to detect any tendency towards swimming movements of the gills before the time of hatching, although the embryos were under observation for six or more hours every day, and especial attention was paid to this point. This absence of swimming movements is rather remarkable in view of the fact that all the embryos begin swimming immediately after hatching

In addition to the swimming movements the complex "gill-scraping” reflexes are absent, according to my observations, in embryos prior to the time of hatching. Certain of these reflexes have been described by Miss HYDE (1. c. p. 432, and Fig. 3). There also occur in adult Limuli, under certain conditions, complex gill-scraping movements of the sixth legs. I

[ocr errors]
« PreviousContinue »