Journal of Morphology, Volume 6

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Ginn & Company, 1892
 

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Página 441 - ... streak of mammalian and avian eggs ; and conversely, we find identical forms of cleavage leading to fundamentally different results ; for example, in the egg of the polyclad as compared with that of the mollusc or the annelid, where " cells having precisely the same origin in the cleavage, occupying the same position in the embryo, and placed under the same mechanical conditions, may nevertheless differ fundamentally in morphological significance.
Página 322 - The system of branchial sense organs and their associated ganglia in Ichthyopsida. A contribution to the ancestral history of vertebrates. Quart. Jour. Micr.
Página 367 - gastrula' cannot be taken as a starting-point for the investigation of comparative organogeny unless we are certain that the two layers are everywhere homologous. Simply to assume this homology is simply to beg the question. The relationship of the inner and outer layers in the various forms of gastrulas must be investigated not only by determining their relationship to the adult body, but also by tracing out the cell-lineage or cytogeny of the individual blasto meres from the beginning of development.
Página 299 - Helmholtz's conclusion, which came into •wide acceptance as a basic principle of sound perception, was that "the quality of the musical portion of a compound tone depends solely on the number and relative strength of its partial simple tones, and in no respect on their differences of phase
Página 393 - Transition to the Bilateral Period. As far as the development of the permanent organs is concerned, the transition from the spiral to the bilateral type of development is remarkably abrupt." It may be mentioned, that at the close of the spiral period there are, according to Wilson, 38 blastomeres present. That is to say, the majority of them are products of the fifth cleavage. On page 444 he asks „what is the significance of the spiral and bilateral forms of cleavage, and where lie the...
Página 273 - ... arrive in the sensory cells of the brain, and there produce, not sound again, of course, but the sensations of sound, the nature of which depends, not upon the stimulation of different sensory cells, but on the frequency, amplitude, and form of the vibrations coming into the cells, probably through all the fibres of the auditory nerve.
Página 365 - Thatsachen nicht entsprechender, Begriff. Was man bisher so nannte ist entweder die Summe unabhängiger heterogener Anlagen, die im Bereich der primären Keimblätter entstehen, oder eine einzige Anlage eines bestimmten Gewebes oder Organs, die eventuell theilweiser Umbildung unterliegt. Am häufigsten sind mächtige ektodermale Muskelanlagen und paarige Anhänge des Urdarms zum mittleren Keimblatt gemacht worden. Die Frage nach der Homologie des sogenannten Mesoblasts in den verschiedenen Thierklassen...
Página 444 - The meaning of the bilateral cleavages in themselves is perfectly obvious. They are the forerunners of the bilateral arrangement of parts in the adult ; and, as such, their explanation belongs to the general problem of bilateral symmetry, which need not be considered here. The all-important point is that the bilaterality does not appear at the beginning of development. It appears only at a comparatively late stage, and by a change so abrupt and striking as to possess an absolutely dramatic interest.
Página 154 - ... by Allis, gives us the key to the solution of the problem of the homologies of the parts of the internal ear. In this fish the inclosure of the canals and the formation of the pores and tubes, while it is undoubtedly the primitive process, is essentially a simple and regular process, and when it is fully carried out the canals arise in separate sections, each of which contains a single senseorgan. In the young Dog-fish, in which the canals have not begun their development, the sense-organs lie...
Página 231 - Although ontogenctic evidence seems to lead to the conclusion that the auditory organ arose by the invagination of a single superficial sense-organ, it is by no means certain that this is true ; for there are certain facts of comparative anatomy and certain phylogenetic considerations which point to the conclusion that the auditory organ has arisen by the bringing together of two originally distinct sense-organs which were together sunk below the surface.

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