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

  • George Linius Streeter
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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    normally buds out from the caudal border of the saccule in these cases is found extending forward toward the prootic ganglion. The ear vesicle, however, is not in all respects independent of the surrounding structures. Some experiments which are reported below, indicate that its position in reference to the brain, ganglion masses and the surface of the body is determined by the environ- ment itself; it may be rotated in any direction, and nevertheless it eventually develops in the normal attitude, with the saccule toward the ventral surface, the semicircular canals toward the dorsal surface, the lateral semicircular canal being toward the lateral surface, and the endolymphatic appendage toward the brain. The experiments were carried out on larvae of Rana sylvatica and Rana pipiens, and the operating stage was the same that was used in previous experiments.* The time is just at the close of the non-motile stage, and the epithelial ear consists of an invag- inated cup-shaped mass of cells just in the process of being pinched off from the deeper layer of the skin, with the edges turning in to form a closed vesicle. For simplicity the term “ear vesicle” will be used even though the closure is not yet complete; the attempt to distinguish between auditory cup and auditory vesicle does not seem to be justified for the present purposes. The technique of the operations was also the same as that described in the previous paper. Notes were made on the behavior of the animals, and at the end of from four to six weeks the specimens were preserved in a chrome-acetic mixture, cut in serial sections, and stained with h:ematoxylin and congo red. With certain specimens the ear vesicle, adjacent ganglia, and a portion of the central nervous sys- tem were reconstructed after the Born wax plate method. Eleven such models were made, and photographs of some of them are reproduced in Figs. 2, 3 and 6. With the aid of these models it was possible to identify relations and detailed features of the laby- rinths that otherwise could not have been recognized. The morphological features of the experiments will be first con- sidered, and the behavior of the animals and its relation to equilib- rium will be treated separately in the latter part of the paper. ^ Streeter ’o6: /. c., Fig. 3, p. 547.
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