Some factors in the development of the amphibian ear vesicle and further experiments on equilibration / by George L. Streeter.

  • Streeter, George Linius, 1873-1948.
Date:
1907
Catalogue details

Licence: In copyright

Credit: Some factors in the development of the amphibian ear vesicle and further experiments on equilibration / by George L. Streeter. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    DETERMINATION OF POSITION OF THE EAR VESICLE The conclusion that the attitude of the developed labyrinth, the position of its canals and various chambers, is determined by its environment is based on seventeen experiments in which the ear vesicle was loosened from its normal situation and placed in an abnormal attitude, and the specimen then allowed to continue in its development. At the end of a month examination showed that the labyrinth had become differentiated with varying degrees of completeness, and in each instance had developed in normal rela- tion to the surrounding structures. Rotation in Two Directions. In eight of these experiments the ear vesicle was rotated i8o° around both its vertical and transverse axes, so that it was turned face inward and upside down; or, in other words, its lateral or invaginated surface was toward the brain and its ventral border was where the dorsal border should be, the maxi- mum displacement. After this procedure the wounds healed within a few hours, and the larvie were reared up to the fourth or fifth week, when they were killed and cut in serial sections. The labyrinths of five specimens were reconstructed. Before describ- ing them reference should be made to the normal condition of the labyrinth at this age. A reconstruction of a normal one with its adjacent structures is shown in Fig. i. From the reconstruction of a normal specimen it can be seen that the three semicircular canals have individual characteristics by which they can be separately identified; such as the Y-shaped union of the anterior and lateral canals, and the overlapping of the caudal end of the lateral canal by the posterior canal, and the junction of the posterior and anterior canals to form the crus com- mune. The differentiation between utricle and saccule is not yet complete, but the part that is to become saccule is so labeled. From the caudal border of the saccule can be seen a small pocket budding out which constitutes the lagena or primitive cochlea. Directly median to the crus commune is the endolymphatic append- age, consisting of a small duct leading from the main labyrinth chamber up between the labyrinth and brain to a rounded pouch, the saccus endolymphaticus. In their histology, as well as in