. Principles of economic zoo?logy. Zoology, Economic. 224 BRANCH CHORDATA cretions would also imply a sense of smell, but these may be wholly for defense. The nostrils^ of toads and frogs can be closed by special muscles. The lateral hne of the tad- pole disappears in the adult. It seems that whatever senses may be located in the lateral line, they are ineffectual outside of water. In most amphibians there is an internal ear which opens by one or two openings into the mouth, back of tlie openings from the nostrils. None of them have any outside opening to the ear, but most of the higher forms
. Principles of economic zoo?logy. Zoology, Economic. 224 BRANCH CHORDATA cretions would also imply a sense of smell, but these may be wholly for defense. The nostrils^ of toads and frogs can be closed by special muscles. The lateral hne of the tad- pole disappears in the adult. It seems that whatever senses may be located in the lateral line, they are ineffectual outside of water. In most amphibians there is an internal ear which opens by one or two openings into the mouth, back of tlie openings from the nostrils. None of them have any outside opening to the ear, but most of the higher forms (Aiiura) have a drum-cavity and a tympanic membrane over it, lying at the surface. A single bone, the columella, lies across the middle ear and has one end against the tympanum. There is no cochlea, or at least a very rudimentary one; hence it does not seem possitjle that the frog can detect differences in pitch. Perhaps this accounts for his monotonous song. Yerkes found that frogs "straightened up and raised the head as if list- ening when other frogs croaked or splashed into the water," l)ut found it impossible to make them respond in any way to any noise he himself made so long as he remained invisible.'- He thinks they depend on sight for the. Fig. —Brain and spinal cord of frog {x about 2): u, Cerebral hemisphere; b, olfactory lobe; c, eye; d, thalamencephalon; e, optic lobes; f, cerebellum; g, medulla oblongata; h, fourth ventricle; i, spinal cord; I, Olfactory nerves; II, optic nerve; III, oculomotor nerve; \\, patheticus; \', fifth nerve; VII, facial nerve; VIII, auditory nerve; IX, glossopharyn- geal nerve; X, vagus nerve; 1-10, first to tenth spinal nerves; 2 and .3 unite to form (he brachial, :ind 7, S, and 9, to form the sciatic plexus. (Shipley and McBride.) 1" There seems to be no experimental proof of specific taste or smell among amphibians or ;—Washburn. - Linville and Please note that these images are extracted fr
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