Origin of the electric tissues of Gymnarchus niloticus.

  • Dahlgren, Ulric, 1870-1946.
Date:
1914
Catalogue details

Licence: Public Domain Mark

Credit: Origin of the electric tissues of Gymnarchus niloticus. Source: Wellcome Collection.

Provider: This material has been provided by the Augustus C. Long Health Sciences Library at Columbia University and Columbia University Libraries/Information Services, through the Medical Heritage Library. The original may be consulted at the the Augustus C. Long Health Sciences Library at Columbia University and Columbia University.

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    text-fig. 5) to be sectioned as follows: First, from in front of the anus to a point about 26 vertebral segments posteriorly. The last three segments of this portion were sectioned transversely and serially (region A-^ while the remaining anterior part was sectioned vertically and longitudinally (region A). Another portion of 19 vertebral segments further caudad was removed and its posterior two segments sectioned transversely (regional), while the anterior part was cut as before in vertical, longitudinal sections Fig. 5.—Outline of body of an embryo of Gymnarchus nine days old. Transverse lines and letters indicate parts sectioned for study. For explanations see text. (Copied from Assheton in The Work of John Samuel Budgett.) X S. (region B). A third part, of 18 more vertebral segments, was treated in the same way, except that no transverse sections were taken and the entire piece was cut vertically and longitudinally (region C), while the remaining portion or tail-tip was cut serially in transverse sections and forms a series (region D). Figure i, plate i, shows a transverse section through the body a rather short distance from the extremity of the tail or at a point where we are sure that the electric organ will be well developed a little later in life. It may be thought that such a section could be taken for study to better advantage in a more anterior position on account of the earlier anterior development just discussed, but it must be taken into account that the tail segments are being added and are still growing rapidly at this age, that they are very short and very crowded, and therefore the location of this section is, in reality, fairly well forward in the future electric spindles. Conditions were much the same in region C. This section shows a good development of muscle fibers as indicated by the shaded area. As is usual in vertebrates, the most advanced stages of muscle-cell development are to be seen at the lateral periphery of the myotome. Here, at the point indicated in figure i, plate i, by the dotted line, a layer of the outer muscle cells, two or three deep, has acquired an average of about 26 myofibrils (an average of 14 counts). These are grouped in one (fig. 2, plate I, B and C) or sometimes two bundles in the cell (fig. 2, plate i, A) and their correct spacing and their thickness and staining power indicate muscle cells of normal development and good functional activity. The remaining and inner muscle cells of the myotome, forming its larger bulk, show, as one examines them successively farther inward (toward the median line), a series of earlier stages, until at many points on the inner edge of the