Outlines of comparative anatomy, presenting a sketcxh of the present state of knowledge of the progress of discovery, in that science. Designed to serve as an introduction to animal physiology, and to the principles of classification in zoology / By Robert E. Grant ... Containing part first, organs of relation or of animal life, and part second, organs of vegetative or organic life.

  • Grant, Robert E. (Robert Edmond), 1793-1874.
Date:
1841
Catalogue details

Licence: Public Domain Mark

Credit: Outlines of comparative anatomy, presenting a sketcxh of the present state of knowledge of the progress of discovery, in that science. Designed to serve as an introduction to animal physiology, and to the principles of classification in zoology / By Robert E. Grant ... Containing part first, organs of relation or of animal life, and part second, organs of vegetative or organic life. Source: Wellcome Collection.

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    unite to thicken the parietes of the general cell, two or more nuclei are often found within the same cell, and the nuclei generally retrograde in their development, or entirely dis¬ appear, when the cells they produce have arrived at their maturity. The successive strata of epidermic cytoblasts are most accumulated, and retained, in a condensed form, on parts of the skin most exposed to pressure and friction, as on the palmar and plantar surfaces of the extremities, and on the whole surface of thick-skinned naked animals, as rhinoce- roces, hippopotami, manati, and other pachyderma and ceta¬ cea. The difference of colours in the contained parasitic pigment-cells of the epidermic cytoblasts, which are most vivid and most lively in the soft, loose cytoblasts of the rete mucosum, gives rise to the varied hues of all the tegumen¬ tary parts of animals. In the interior even of these parasitic pigment-cells, are sometimes seen numerous other minute cells in active movement. The colour of the pigment-cells often varies in different parts of the skin, giving rise to cor¬ responding differences in the colour of the hairs, spines, and other epidermic developments ; their excess produces the intense colour of the rete mucosum of the negro, and other deeply-coloured animals; their deficiency produces the various tegumentary peculiarities of albinos; and the ephemeral existence of these coloured parasites, causes the outer strata of epidermis to be shed colourless, from the most deeply coloured skins of animals, as salamanders, serpents, and negros. The epidermis is already a thick layer on the pal¬ mar and plantar surfaces of the extremities in the early con¬ dition of the embryo, and the coloured parts of the integu¬ ments of quadrupeds are distinctly marked at an early period of the foetus in utero. The cytoblasts of the epithelium, at the exterior open¬ ings of mucous cavities, have mostly the same flattened form and stratified arrangement as in epidermis, as seen on the interior of the nostrils, the lips, the mouth, the tympanic cavity and the mastoid cells, and on the surface of the con¬ junctiva and cornea, where they were observed and described by Leuwenhoek, as forming a hundred strata of superim¬ posed scales ; but in most other parts of the mucous surfaces they present a conical or cylindrical form, are compactly