Studies from the Biological Laboratory, Edição 1N. Murray, Johns Hopkins University, 1879 |
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activity adult animal Annelids anus appearance become blastopore body body-cavity Brachiopods branchia central cells centre changes ciliated corpuscles curve digestive cavity digestive tract dorsal dorsal surface ectoderm embryo endoderm experiment fibres Figure 14 food yolk foot formative pole Fort Wool frog gastrula gastrula mouth gland granular head vesicle hyphæ increase integument interval of stimulation invagination irritation Lankester larva layer lever Lingula lobes lophophore lumbar vertebræ lungs macromeres mantle margin membrane ment mesoderm millimetre minute Mollusca movements muscle nearly nerve normal observations oesophagus opaque opening optic optic lobes oral end organs ovoid cells oyster pair period Plate polar globule Polyzoa portion posterior respirations respiratory rhythmic sciatic seen shell shew shown in Figure side single contraction specimens spherules sphincter spores stage shown stomach sweat tentacles tetanic throat tion tracing transparent valve velum ventral ventral surface W. K. BROOKS
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Página 17 - This layer is seen in the section to be pushed in a little toward the upper layer, so that the lower surface of the disk-shaped embryo is not flat, but very slightly concave. This concavity is destined to grow deeper until its edges almost meet, and it is the rudimentary digestive cavity. A very short time after this stage has been reached, and usually within from two to four hours after the eggs were fertilized, the embryo undergoes a great change of shape, and assumes the form which is shown in...
Página 94 - The divergence of the Brachiopods, having been attained in more ancient times, a few degraded features are yet retained, whose relationships we find in the lower Vermes; while from their later divergence the fixed and cephalized Annelids are more closely allied to present free Chaetopods.
Página 18 - Fig. 33 is a sectional view of such an embryo. It is seen to consist of a central cavity, the digestive cavity, which opens externally on the dorsal surface of the body by a small orifice, the primitive mouth, and which is surrounded at all points, except at the mouth, by a wall which is distinct from the outer wall of the body. Around the primitive mouth these two layers are continuous with each other. The way in which this cavity, with its wall and external opening, has been formed, will be understood...
Página 16 - Figures 24, 25 and 26, we have a layer of small cells wrapped around the greater part of the surface of a single large spherule, and the series of figures shows that the latter is the spherule which is below in Figure 6.
Página 22 - Fig. 45 it is seen in surface view, drawn in between the shells, and with its cilia folded down and at rest, as they are seen when the little oyster lies upon the bottom. • "The two shells grow rapidly, and soon become quite regular in outline, as shown in Figs.
Página 62 - The same egg fwo minutes later. It is now elongated ; one end is wider than the other, and a transparent area at the broad end marks the point where the polar globules are about to appear. At the opposite end the external membrane is wrinkled by waves which run from the nutritive towards the formative pole in rapid succession for about fifteen seconds. Figure 3. — The same egg two minutes later. Figure 4.
Página 17 - Fig. 25, and a lower layer of much larger, more opaque cells, g, which are to become the walls of the stomach, and which have been formed by the division of the large spherule, o, of Fig.
Página 18 - This stage of development, in which the embryo consists of two layers, an inner layer surrounding a cavity which opens externally by a mouth-like opening, and an outer layer, which is continuous with the inner around the margins of the opening, is of very frequent occurrence, and it has been found,, with modifications, in the most widely separated groups of animals, such as the star-fish, the oyster and the frog, and some representatives of all the larger groups of animals, except the Protozoa...
Página 10 - ... female is necessary to the fertilization of the latter and the consequent hatching of living oysters. The number of male cells which a single male will yield is great beyond all power of expression, but the number of eggs which an average female will furnish may be estimated with sufficient exactness. An unusually large American oyster will yield nearly a cubic inch of eggs, and if these were all in absolute contact with each other, and there were no portions of the ovaries or other organs mixed...
Página 28 - The living and dead shells of the adult oysters furnish the best surfaces for the attachment of the young, and for this reason the points where oyster beds are already established are those where the young have the most...