Imágenes de páginas


[ocr errors]




Corresponding Secretary.
SAMUEL KNEELAND, JR., Recording Secretary.

The several Standing Committees were appointed as fol-

Rumford Committee.


HENRY L. Eustis,

Committee of Publication. JOSEPH LOVERING, Louis AGASSIZ,


Committee on the Library.


The following gentlemen were chosen Members of the Council for nominating Foreign Honorary Members, viz. :


of Class I.

of Class II.

of Class III. NATHAN APPLETON, Professor Gray presented a paper entitled, “ Caroli a Linné ad Bernardum de Jussieu ineditæ, et mutuæ Bernardi ad Linnæum Epistolæ ; curante Adriano de Jussieu.” Referred by the Publishing Committee. VOL. 111.


The following Foreign Honorary Members were elected :

In Class I. Section 2, Professor C. A. F. Peters, of Königsberg.

In Class III. Section 1, Professor C. Mittermaier of Heidelberg.

In Class III. Section 2, August Boeckh, of Berlin.
In Class III. Section 2, Professor R. Lepsius, of Berlin.

In Class III. Section 2, Chevalier Bunsen, Prussian Ambassador, London.

In Class III. Section 3, G. Grote, of England.

William Raymond Lee was elected a Fellow of the Academy, in the Section of Technology and Engineering.

On motion of Professor Agassiz, it was voted, that the next monthly meeting of the Academy be held on the third Tuesday of June, at half past 7 o'clock, P. M.

Three hundred and eighty-first meeting.

June 21, 1853. — MONTHLY MEETING. The PRESIDENT in the chair.

The Corresponding Secretary read a letter from William Raymond Lee, Esq., accepting membership of the Academy; and a letter from the Hon. Timothy Walker, of Cincinnati, acknowledging the reception of the resolutions passed at the annual meeting of the Academy on the death of his brother, Sears C. Walker, Esq.

Professor Agassiz made a communication on the family of Cyprinodonts, of which he had discovered some new generic forms, and twelve new species, in a recent visit to the Southern States. The differences between the sexes are often so marked in this family of fishes, that the males and females have been described under distinct genera. At a former meeting he had mentioned an error of this kind, and he was now able to correct another. Pæcilia and Mollienisia, described as distinct genera by Cuvier and Valenciennes, he had ascertained to be the male and female of the same species, the former being the female and the latter the male. When young, both sexes look exactly alike. He had established a new genus, Heterandria, in which the sexual differences were very remarkable; the position and shape of the ventral and other fins being quite different, which he showed by diagrams. The habits of these fishes, living in immense numbers, crowded together in very shoal water, enabled him to explain a figure represented in the fifth volume, Plate 41, of his Fossil Fishes, in which the great number of individuals was remarkable ; and the knowledge of the sexual differences renders unnecessary any hypothesis to account for supposed displacements of fins, or the occurrence together of different species. He also had established a new genus, Zugonectes, in which no sexual differences existed.

Dr. Burnett read a paper “On the Signification of Cell-segmentation, and the Relations of

this Process to the Phenomena of Reproduction. “ The phenomena of the segmentation of cells are intimately connected with many of the highest conditions of organization, and it becomes a question of no little interest in physiology, what interpre. tation is to be put upon this process of segmentation. .

“ By the term Cells, I include, not merely the elementary constituent particles of organized forms, but also ova, for it now appears pretty definitely settled that the ovum is, morphologically, only a cell; of this point, deducible from the observation of various naturalists upon the elementary condition of ova in different lower animals, I have recently satisfied myself, from investigations upon the ovaries of insects. Moreover, the segmentation of the ovum as preliminary to the formation of a new individual involves physical phenomena not in the least different from those of this process occurring with simple individual cells.

“ This process consists, as is well known, in the successive halvings of the nucleus of a cell, the number of the parts produced being, therefore, whether greater or less, the multiple of two in a geometrical progression. Its physical conditions are, briefly, first, a sulcation of the cell membrane at one point; the concavity thus commenced gradually deepens and extends through the cell, ending in the complete halving of the cell, together with its contents; each of the halves thus formed undergoes the same process of division, and so on to a greater or less number of subdivisions, the products being, not seg. ments of a sphere, as would be the case from the division of inorganic matter, but miniature cells, resembling, in every particular except mere size, the original cell. This spontaneous division and subdivision of organic matter, by which definite particles reproduce their kind, lies at the very foundation of the successive continuation of all specific organized forms in the vegetable and animal world.

“ Until late years, this process of segmentation was supposed to belong exclusively to the impregnated ovum, and to be the index of its state of fecundation. Recent researches in histology, however, have shown, not only that it is a very common phenomenon with most individual cells, but also that it may occur in the ovum before fecunda. tion ; that is, is not the direct sequela of this last. In epithelial cells, as also those belonging to various morbid growths, I have watched this process occurring exactly as with the ovum; and in the ova of the common codfish (Gadus morrhua), before expelled from the ovaries, and therefore before impregnation, I have seen phenomena indicating that the segmentation of the vitellus had already commenced.

“ But we will examine the details of this process as occurring where they are mostly completely expressed, in the impregnated egg. Throughout the entire organized world, the development of new individual forms from the ovum which has its origin in a proper sexual organ, is always preceded by this process, to a more or less complete extent; this segmentation may, indeed, go on to a certain extent before fecundation, as already remarked, but its continuance ending in the evolution of a new individual form is invariably dependent upon the act of fertilization by the male product, or sperm. I wish to insist upon this point in reference to some remark soon to be made. It may be said further, that not only is the whole individual formed out of the segmentation products, but at those points of the animal which contain tissues of the noblest function is always the most complete ; such, for instance, is the case with the line of the nervous centres.

“ The sperm-cell being the analogue of the ovum, these same phenomena, just described, are observed to precede the formation of the spermatic particle, and I can confidently affirm that no spermatic particle is produced without the occurrence of these preliminary processes.

“ With such data, and which are, indeed, all we possess, we ask, What is the physiological signification of this fissurating process in cells ?

“ To this I would reply, that it seems to be simply an expression of a vitalizing act, - a means by which cell-particles are extended or reproduced on the one hand, and, on the other, by which crude materials of organized matter are kneaded or worked over for the formation of tissue in distinct individual beings.

“ Thus with simple cells, with the unimpregnated ovum, and with the sperm-cell, this process occurs, leading to a mere reproduction or multiplication of the cells, and which may continue to a greater or less extent ; while, on the other hand, with the impregnated ovum, these processes, although physically the same, are directed from the fecundating act towards a definite end, that is, the formation of tissues which compose a new being.

“In this connection, I may well allude to those anomalous phenomena, the successive reproduction of individuals without the aid of the male influence, as occurs with the Aphides. The general character of this form of multiplication of individuals is well known in science; but what I wish to insist upon now is, that these phenomena, as I have recently studied them, have nothing antagonistic to the doctrines of cells just advanced, for the so-called eggs of the viviparous Aphides, and which develop without the aid of the sperm, are, in my opinion, not true eggs, but are rather buds, and therefore development here occurs by a kind of internal germination. But this subject of the development of Aphides in its details, as I have recently enjoyed the opportunity to successfully study it, I intend to present at the next meeting.

Cell segmentation, therefore, is a vital act of cells as organic particles, and is primary instead of secondary in the grand acts of true generation.

“ This subject, important as it is in itself, has a wide physiological bearing. If such phenomena invariably attend the production of a new individual form from a true egg, can there be, as has recently been advanced by several physiologists, animals composed of only a single cell ? To this question the answer would be in the negative ; and such forms would seem to me no more worthy to be regarded as true animals, than would be the resultant products of segmented epithelial cells.

“On the very lowest confines of the animal kingdom there are,

« AnteriorContinuar »