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Principles of general and comparative physiology : intended as an introduction to the study of human physiology : and as a guide to the philosophical pursuit of natural history / by William B. Carpenter, M.D.

  • Carpenter, William Benjamin, 1813-1885.
Date:
1841
Catalogue details

Licence: Public Domain Mark

Credit: Principles of general and comparative physiology : intended as an introduction to the study of human physiology : and as a guide to the philosophical pursuit of natural history / by William B. Carpenter, M.D. Source: Wellcome Collection.

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    during germination. From the centre only of this primary frond, as in the Ferns, are the permanent structures evolved ; the peripheral portion soon disappears. § § 599, 600. 5. In all tribes of Animals, except the Sponges, there now seems reason to believe, that two sets of organs, as in the Phane- rogamic Plants, are concerned in the Reproductive process. One set furnishes the Spermatozoa, which are probably to be regarded as analogous to pollen-grains,—containing the granular germs of new cells, and having the power of conveying them to the ovules; their power of movement is not an evidence of their independent vitality, but is rather to be compared with that which cilia possess. The ovules are analogous in general structure to those of Plants ; being principally occupied with nutritious matter—the yolk,—for the support of the new fabric. It is curious that, in Plants as well as in Animals, a cellular organisation, which afterwards disappears, should be visible in this matter, previously to the introduction of the germ into the midst of it. §§ 604-613. 6. The earliest nisus of the development of the germ in Animals, is the extension of the periphery of the mass of cells first produced, into a membrane, which encloses the yolk. An additional layer is subsequently formed internally to this, pro- ceeding from a part of the germinal mass nearer to its centre. The sac thus formed is the simplest condition of a stomach,—the most characteristic structural distinction between Plants and Animals. In the Raptrara, the whole of this first-formed struc- ture is persistent ; the exterior layer constituting the permanent envelope of the body, and the interior the lining of the stomach. §§ 614-620. 7. In the Articutata and Mo.tusca, also, the germinal membrane, which is an extension from the peripheral portion of the first-formed mass of cells, remains as a component of the perfect structure ; its outer layer forming the integument, and its inner layer giving origin to the viscera. From the central cell of the germinal mass, however, the organs of animal life originate ; the predominance of these early manifests itself in the Articulata ; as does that of the organs of nutrition, developed from the peripheral portion of the germinal mass, in the Mollusca. § § 631, 632, 634, 637, 640. 8. In the Vertesrata, the whole of the first- ene structure is completely transitory in its character, like the cotyledons of Plants. It serves to absorb the nutriment supplied by the yolk,