. The biology of the amphibia. Amphibians. THE SENSE ORGANS AND THEIR FUNCTIONS 337 L. P H. C. by a movable tectorial membrane (Fig. 123) and would seem to serve as the chief organ of hearing. This organ is lacking in many perennibranchs and is best developed in Salientia where it lies in a small evagination of the lagena. A second hearing organ of Salientia and of certain primitive urodeles including Ambystoma (Norris, 1892) is the macula neglecta which in these forms is also covered with a tectorial membrane. The papilla basilaris alone of the sense areas was destined for elaborate specializ
. The biology of the amphibia. Amphibians. THE SENSE ORGANS AND THEIR FUNCTIONS 337 L. P H. C. by a movable tectorial membrane (Fig. 123) and would seem to serve as the chief organ of hearing. This organ is lacking in many perennibranchs and is best developed in Salientia where it lies in a small evagination of the lagena. A second hearing organ of Salientia and of certain primitive urodeles including Ambystoma (Norris, 1892) is the macula neglecta which in these forms is also covered with a tectorial membrane. The papilla basilaris alone of the sense areas was destined for elaborate specialization in phylogeny, for it alone has de- veloped into the organ of sharp hearing found in mammals and birds. Plate (1924) suggests that this may have been due to its more favorable position near the perilymphatic duct and near a thin place in the sacculus wall which would readily permit the transference of vibrations s. c from the perilymph to the endolymph. An advance of obscure func- tional significance over the conditions in the fish ear is found in the perilymphatic duct. This grows out from the mesial wall of the sacculus and into the brain cavity. In the Salientia it forms with its mate a ring around the hind brain, and continues posteriorly as an unpaired sac along the spinal cord as far as the seventh vertebra. Its wall, which may become partitioned by many septa, secretes a cal- careous fluid which distends the sac to form a series of white diverticula overlying the spinal ganglia. It has been said that this enormous supply of calcium carbonate was utilized by grow- ing bone, but Herter (1922) showed that tadpoles deprived of these sacs grew as well as the controls. Possibly the vertebral sacs transmit vibrations impinging on the back. They are lack- ing in Bombina and Discoglossus, although present in most higher Salientia, (Whiteside, 1922). The endolymphatic sacs of each side may or may not fuse in the urodeles and the type of modifica-. Fig. 123.—Cross-section th
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Keywords: ., bookcentury1900, bookpublishernewyorkmcgr, booksubjectamphibians
