EMBRYOLOGY.'

Movements of Blastomeres. In a copiously illustrated and extensive paper on the cleavage of Ascaris megalocephala Otto zur Strassen' lays special emphasis upon certain movements of the cells of the embryo.

In the living egg most remarkable rearrangements of the material are easily seen when the first four cells glide over one another. In later stages changes in form are traced to movements of the cells that must have taken place though not actually seen but inferred from a very detailed study of preserved material. The author confined his attention chiefly to the ectodermal layer of cells and knowing the pedigree of a very large number of them was able to affirm that the changes in shape that the embryo exhibits are due, in part at least, to an actual migration or rearrangement of cells. Cell division and surface tension are not the only factors concerned in this change of position of the cells; there must be some individual movement of certain cells.

This movement of the cells is regarded as being of the same nature as that observed by Roux in the isolated cells of the frog's egg and is, therefore, designated Cytotropism.

The production of form in the development of the Ascaris embryo has then this important factor-a power of cells to move towards one another and thus change the shape of the entire mass. This movement is in addition to any purely mechanical movements due to surface tension and is due either to attraction between cells or to repulsion between cells. In either case it is assumed that chemical influences are at work: that this movement arises from chemotactic strains.

The movements are much restricted in that a cell travels its own length at most and is never free from its sister-cell. In fact the two cells that arise from the division of one remain connected and are not to be separated by any intrusion of migrating cells and the author thinks that the movements are probably even more restricted in being merely the rearrangements of two groups of such sister-cells both derived from one parent, being merely readjustments of four grandchildren of one cell! The entire ectoderm may then be regarded as a mosaic of such sets of families of four, each having its own internal readjustments.

Edited by E. A. Andrews, Baltimore, Md., to whom abstracts reviews and preliminary notes may be sent.

' Archiv f. Entwickelungsmechanik, 3, 1896, pps. 27-101, 133--188, Pls. V--IX.

Moving pigment in Eggs.-In a carefully illustrated account of the cleavage of the Planarian, Polycharus caudatus Mark, Dr. E. G. Gardiner describes most remarkable changes in position of peculiar, algalike, pigment bodies which color the eggs orange-red for a certain period. These bodies appear in certain cells and then others, they lie along the lines where cleavage is to take place.

They move up from the centre of the egg to the surface and move from place to place.

Fertilization.-By the use of nitric acid Kostanecki and Wierzejski find that the so-called achromatic substance may be demonstrated with remarkable clearness in the eggs of the pond snail Physa fontinalis. In a detailed description' of radiations, or stars, of this substance seen during the process of maturation of the egg and during fertilization, illustrated by many remarkable figures of reconstructed sections, the authors give the facts that lead them toward the following hypothetical conception of the true nature of the process of fertilization.

The object of fertilization is the union of the nuclei; but the necesary condition to make this of avail is that the egg be able to continue to divide, to undergo cleavage. This power is brought to it by the new nuclear part of the sperm.

Each sexual cell needs to be supplemented by what the other has and it itself is deficient in. This lack is in the protoplasm.

The egg has large amounts of nutritive material while the sperm has none. The former has thus relatively too little protoplasm to continue dividing by itself. During maturation, by dividing twice to form polar bodies, the egg uses up its remaining power of division and must have this added to it again if it is to cleave at all.

What the sperm brings in to replace the exhausted cleaving powers of the egg is the connecting piece of the sperm, the portion near the head or nucleus, that contains achromatic material centered on the centrosome or speck next the head. This material is the remnant from the achromatic figure of the last cell division in the formation of sperms.

This material is conceived of as concentrated and not, as yet, recognized till it gets into the egg; then it swells up and extend in radii as an umbrella unfolds. As the sperm revolves through 180° after entering the egg the middle piece preceeds the sperm head or male nucleus in its journey towards the female nucleus. The middle piece appears as a star centered about the centrosome and rapidly grows in all direction 3 Journal of Morphology, XI, pp. 155–171.

Archiv. f. Mik. Anat., 47, 2, Apl, 1896, pps. 309-379, Pls. 18--20.

by "assimilating" the net-work of the egg. Thus the star, so remarkably distinct in these snail eggs, about the centrosome of the sperm is to be regarded as at first of male origin and then as gradually getting control of the net-work protoplasm, or the archoplasm, of the egg so that it is eventually the centre of an entire rearrangement of this egg material focussed about the male centrosome.

The centrosome next the famale nucleus disappears and the star about it is "assimilated" by the star that arose about the male nucleus. Sooner or later the male star and centrosome divide to furnish the twocentered system concerned with division of the cleavage nucleus. The male and female nuclei unite to make the cleavage nucleus and the two protoplasmic stars do all that remain to be done in the subsequent cleavage.

The substitution of the new male system for the effete female system of radiate protoplasm is regarded as so complete that the chromosomes in the female nucleus become subjected to the domination of the male system by the growing male radii attaching themselves to these chromo somes by a process of " assimilation" of the old connections, that the author believes to exist between the female chromosomes and the female centrosomes. It is assumed that this male system is all along connected with the chromosomes of the sperm head and that the contractoin of the radii draw the sperm head toward the female nucleus.

Along with the reduction of the chromosomes in both egg and sperm there is probably a reduction in the mass of so-called achromatic substance so that in fertilization there may well be restitution of the normal amount by a mutual supplying of the deficiency.

It will be seen that this conception of the process of fertilization is that of Boveri except that the centrosome is regarded as of no importance and the surrounding, radiated protoplasm becomes the essential factor for cell division. The authors follow Heidenhain in regarding the centrosome as merely the point of insertion of that active, contractile part of the cell that radiates out from this centre.

PSYCHOLOGY.'

The Effects of Loss of Sleep.-Prof. Patrick and Dr. Gilbert, of the University of Iowa, have reported in the Psychological Review some experiments on this problem. Three normal subjects were kept awake for a period of ninety nours, without resort to stimulants or other 1 Edited by H. C. Warren, Princeton University, Princeton, N. J..

physiological means. During the four days and three nights of the test they were engaged, as far as possible, in their usual occupations; their meals were of the customary kind, and were taken at the ordinary times, with the addition of a light lunch at about midnight. At intervals of six hours a series of tests was made on each subject, to determine his mental and physical condition. To eliminate the effects of practice, these tests were begun three days before the experiment. The test of the first day of experiment, before any loss of sleep had actually occurred, represent the normal condition of the subject. Tests were also made after the night's sleep that followed the conclusion of the experiment. One of the writers was the first subject. The two other subjects were instructors in the university; the latter were experimented upon at the same time.

Some of the results are of special interest. The reaction time (for sound) showed a gradual increase for two of the subjects, which was masked in the third case by increase of practice; at one period (different in the three cases) the time was considerably greater than earlier or later in the experiment; the mean variation was somewhat above the normal, but not remarkably great. The acuteness of vision, measured by the distance at which a page of print could be distinguished and read, actually increased during the progress of the experiment, and fell off again after the ensuing sleep. The memory test of the two last subjects consisted in committing random series of figures; the time required for this memorizing fluctuated considerably, with a marked lengthening towards the close of the experiment. One of the subjects was unable to memorize the figures at all at two of the last day's tests; he found it impossible to hold the attention upon the task long enough to complete it. The time consumed in adding sets of figures was fairly constant, with two or three exceptions; it was apparently independent of the memory conditions. "Voluntary motor ability," tested by the number of taps that could be made with the finger in five seconds, showed no marked alterations; neither did the susceptibility to fatigue, as tested by continuing this tapping for sixty seconds. The strength of grip, measured on the squeeze dynamometer, fell off from 20 to 30 per cent. at the end of the second day, but afterwards recovered-in two cases fully, in the other partially. The weight of the men remained fairly constant, showing a slight increase towards the close of the period, and the variation of the pulse was within the normal range of daily fluctuations.

The first subject suffered from marked visual hallucinations after the second night. "The subject complained that the floor was covered with

a greasy-looking, molecular layer of rapidly moving or oscillating particles. Often this layer was a foot above the floor and parallel with it, and caused the subject trouble in walking, as he would try to step up on it. Later the air was full of these dancing particles, which developed into swarms of little bodies like gnats, but colored red, purple or black. The subject would climb upon a chair to brush them from about the gas jet, or stealthily try to touch an imaginary fly on the table with his finger. These phenomena did not move with movements of the eye and appeared to be true hallucinations, centrally caused, but due no doubt to the long and unusual strain put upon the eyes. Meanwhile the subject's sharpness of vision was not impaired. At no other time has he had hallucinations of sight, and they entirely disappeared after sleep." Neither of the other subjects experienced these hallucinations.

At the close of the experiment the subjects were allowed to sleep as long as they desired. Tests were made upon the first subject, however, at hourly intervals during the first night, to determine the depth of his sleep. He awoke naturally after ten and a half hours, and remained awake during the rest of the day, but slept two hours more than his normal amount the second night. Of the other subjects, one awoke of his own accord after eleven, the other after fourteen hours' sleep; both felt quite refreshed; they required no extra sleep the next night, and felt no ill effects from the experiment.

It will be noticed that the sleep made up was but a small proportion of the amount lost, viz., 16, 25 and 35 per cent. in the three cases respectively. Two possible explanations for this are offered: either a greater depth of sleep may make up for a lesser duration; or sleep is a relative phenomenon, and the subjects, while apparently awake, were in reality partially asleep at times during the experiment. The authors believe that both of these facts are true, and that they operated together in the present instance. While the subjects were not allowed to go to sleep for an instant, and the slightest tendency to close the eyes was met by active measures, still there were indications of the presence of dreams, in lapses of memory and occasional irrelevant remarks. "It must be understood," say the writers, "that these dreams were instantaneous and the subject as wide awake as he could be kept; but these facts reveal a cerebral condition related to sleep. This hypothesis alone, however, would not seen to account fully for the small proportion of sleep made up. And, indeed, a study of our special tests shows that restoration took place chiefly during the profound sleep following the sleep fast, and took place rapidly. That this sleep was actually more profound, and that the profound part of it was longer than usual, was shown by our experiments in depth of sleep," on one of the subjects.