Ueber doe Anwendung des Capillarelektrometers für das Studium der Muskulären Einzelschwankung / von Prof. Burdon Sanderson.

  • Sanderson, Burdon.
Date:
[1898]
Catalogue details

Licence: Public Domain Mark

Credit: Ueber doe Anwendung des Capillarelektrometers für das Studium der Muskulären Einzelschwankung / von Prof. Burdon Sanderson. Source: Wellcome Collection.

Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.

    32/38 page 26
    appears to arise normally, partly, the nephrostome, from the mesoblast, and partly, the tube, from the epiblast. The historyofthe two series of organs can be traced from the dif- fuse egestion and diffuse ectodermal excretion of the sponges (and partly the Echinoderma) to the eventual extinction of the monocytic egestive organs and a perfection of the excretory organs tili the Vertebrate kidney shews its nephrostomes only in ontogeny in the highest forms, whereas the excretory ducts and tlieir Connection with the vascular System are elaborated to a high degree of perfection (Figs. 5 to 10). The Relationship to Ontogeny. Note I. Reasons have been given for regarding the modifications of the alimentary processes to be the direct originators of other sets of organs, the instances of skeletal and pigmentary organs being taken as typical. If in phylogeny the various organs arise from and are intimately con- nected with, the alimentary processes, then in ontogeny the same will result. The first signs of difierentiation will appear in connection with the susten- tative function, and mechanical ingestive processes will lead the way. Thus ingestive cells wandering in from the monoblastic single layer will give rise to the inner layer, and the diploplastic form. From this inner layer again the ingestive cells give rise to the mesoblast or third layer, and again in the triploblastic type, — by further in-wandering from the mesoblast the skeletal, connective tissue, sexual and egestive organs arise. If all the organs of a type were monocytic throughout life, we might expect this form of development to prevail, but treading as it were upon the heels of the monocytic organs are the polycytic. Thus the polycytic digestive cavity is formed immediately and consequently upon the monocytic ingestion and again, upon this succeeds the polycytic ingestive area or stomodaeum. In a young form in whicli the monocytic ingestion and digestion can be dispensed with, the monocytic mechanical inwandering is hastened out of existence and a complete and direct formation of the polycytic organ' (archenteric cavity) takes place. Thus the complete invagination of a tissue of cells represents the for- mation of the higher type (polycytic) of organ. It follows that the highest type of Metazoan ontogqny is represented by such a form as Amphioxus in which nearly the whole development pro- ceeds upon the principle of tissue invagination, the lowest type being a form in which the organs are differentiated by successive migrating of single cells. In thecase of degeneration, if an organ degenerates, it will advertin mode of origin and in function to a simple type so that the polycytic digestive cavity atrophies in endoparasites; and, in the Tunicata can be selected in- stances shewing a gradation in the degeneration of the body-cavity, migra- tory cells replacing a solid proliferation of cells67. This theory at least offers an explanation of the mechanical ontogenetic processes, supposing them to be of a like nature as the mechanical pro- cesses involved in the successfully maintained mechanical processes of in- gestion, digestion and egestion in the parent organism. 67 A. Willey, Amphioxus and the ancestry of the Vertebrata.
    digitised image 1
    digitised image 2
    digitised image 3