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tion to seek escape, and, in the case of the water tortoises, to seek the water, but as it is pushing over the edge the visual impressions of distance initiate a conflicting motor impulse which causes the animal to draw back. This species manifests fear much more markedly, frequently, and at a less height than does C. picta. On the whole we may say that its behavior to spatial relations would ordinarily be interpreted as indicative of more accurate space perception.

At none of the three heights used in the experiments does Terrapene carolina push over the edge without some hesitation and manifestations of fear. At 30 cm. almost all individuals


Terrapene bauri Taylor

Behavior much the same as that of T. carolina. There is careful inspection of the surroundings and long hesitation. One individual was found that plunged off directly at the height of 180 cm.

Hesitation at

Xerobates polpyhemus

Examination of edge as in T. bauri.
30 cm., and great fear at 180 cm.

Testudo vicina

Not afraid to fall 30 to 50 cm. but careful when at greater heights.

Chelopus insculptus

This species shows greater hesitation than does N. guttata. At 30 cm. it examines the surroundings, and often fails to leave the board.

Emys meleagris

In this species there is some hesitation at 30 cm. but seldom failure to go off. At 180 cm. there is marked fear as in N. guttata, which it very closely resembles in its behavior.


Chelodina novaehollandiae Dumeril et Bibron

Although this form carefully examines the edge and looks at the floor intently it seldom fails to go off. Its actions are very deliberate in most cases.

Trachemys scabra

Many indiduals pay no attention to the edge Lit. tle hesitation even at 180 cm. Behaves much like C. picta.

Podocnemis madagas-
Cariensis Grandidier

No hesitation, no fear at any height at which it was tried. Pays less attention to spatial conditions than any of the species studied.

will leave the board if given plenty of time. This species is more careful than the others in approaching the edge, and it cranes the neck over even more frequently than does C. picta. The inhibition of impulses frequently appears as in case of N. guttata. Unlike the other species, T. carolina notices the spatial relations from its position in the middle of the board, for when 180 cm. above the net an individual is frequently afraid to move, and will remain for a long time just where the experimenter has placed it.

This study of the reactions to space of the three species of tortoises already considered was supplemented by observations of the behavior of several other species at the heights of 30 and 180 cm. In Table III, a summary statement of the results is presented.

Without knowledge of the name of the species, but solely on the basis of the results of the experiments, I classified the species under the three categories Water, Land-Water, and Land Species in order to determine the value of reactions to space as a sign of habits.

Classification in accordance with reactions to space.

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This classification agrees fairly well with what is known of the habits of the forms, except that Chelopus insculptus is a landwater rather than a land species.

The Spatial Worth of Sense Data. For the purpose of ascertaining the relative importance for reactions to space of the visual, tactual, muscular and organic sense impressions some experiments were made with blindfolded tortoises. The eyes, in these experiments, were covered with tin-foil caps which effectually excluded visual stimuli.

C. picta when blindfolded usually rushed off a surface at any height without the least hesitation. There is no evidence,

' from my experiments, that the tactual and muscular impressions received when the legs are stretched over the edge have any inhibitory influence on the movement. From this it is clear that the hesitation of this species observed at heights of 180 cm. is due to visual impressions, not to the unusual organic impressions received. This species at first tries to remove the covering from the eyes by rubbing the fore legs over the head, but failing it soon becomes accustomed to the blindfolded condition.

N. guttata is much disturbed by the obstruction of its vision, and for long periods persistently tries to remove the cap. Most individuals after a time move about freely, but whenever they reach the edge of the board they turn back. Evidently the tactual and muscular impressions inhibit the tendency to move forward. Whereas in case of C. picta, we see the blindfolded animal risking falls which it would not have risked in its normal condition, in N. guttata we see exactly the reverse, for as a rule the animal when blindfolded does not leave the board.

T. carolina does not struggle so persistently to remove the covering as do the other species, but it is inactive when blindfolded. It behaves in general much as it does when placed at a height of 180 cm. above the floor. This indicates that it depends upon vision for guidance in its movements to such an extent that it is not likely to move about much unless it can see clearly.

Visual impressions are of prime importance in the space perception of tortoises, and tactual, muscular and organic data occupy a position of secondary importance. Yet there are

. many reasons for believing that we often underestimate the value in the reactions of simple organisms of that complex mass of sense impressions which we are not as yet able to refer to specific organs. JAMES ('90, II, p. 150) has called attention to a fact that is significant in this connection ; “Rightness and leftness," "upness and downness,” he says, “are again pure sensations differing specifically from each other, and generically from everything else.” We are inclined to lose sight of the organic impressions, and to refer reactions to data received through the so-called special senses. Many experiments have already been made which show that the direction of turning, apart from vision, is extremely important in the motor habits of tortoises and frogs.

I gratefully acknowledge my indebtedness to Mr. SAMUEL Henshaw for suggesting to me the desirability of a comparative study of the space reactions of tortoises; to Mr. THOMAS BARBOUR for valuable assistance in many ways, and for the opportunity of observing the behavior of several foreign species; to Mr. Wm. T. HORNADAY, director of the New York Zoological Park, and to Mr. R. L. DITMARS, Curator of Reptiles, for the privilege of conducting experiments in the Park, and for many courtesies, and to Mr. C. W. Hann for the use of tortoises which were in his possession.


'90. Principles of Psychology. New York. Mills, Wesley. '98. The Nature and Development of Animal Intelligence. London,

307 PP. Small, W. S. '99. Notes on the Psychic Development of the Young White Rat.

Amer. Jour. Psychology, Vol. 11, pp. 80-100. Thorndike, E. L. '99. The Instinctive Reactions of Young Chicks. Psychological Re.

view, Vol. 6, pp. 282-291. Watson, John B.

'03. Animal Education. Chicago, University of Chicago Press. 106 pp.




(From the Neurological Laboratory of The University of Chicago.)

With Plates III and IV. In the course of an investigation on the growth changes in the nerve cells of the white rat, the writer noticed that the nucleus very often had a peculiar shape; the shape being similar to an amoeba exhibiting pseudopodia-like processes along one side.

Careful observation revealed the fact that this peculiar form of the nucleus occurs normally during the period of the early growth and in attempting to explain it we meet several interesting questions of histological as well as physiological importance. The results here reported form a part of a series of observations on the growth changes in the developing nerve cells.

For this investigation, the intrauterine embryos of cat, pig and white rat were used. The present description and drawings are, however, based entirely on preparations from white rat.

Unless otherwise mentioned the description also applies to the cat and pig. The tissue was preserved in a normal salt solution saturated with HgCl; in CarnoY's solution and in GRAF's chrom-oxalic mixture. For the microchemical test for P. and Fe., however, the tissue was fixed advantageously with 95% alcohol. The paraffine sections were made 3 to 6 micra in thickness, and were stained with HEIDENHain's iron-haematoxylin alone or sometimes followed by 1% aqueous solution of eosin and BIONDI-Ehrlich's tricolor stain. Other sections were stained with toluidin blue and eosin.

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