AUDITORY ORGANS. 531 



stalk. At the same time it travels round the right side of the 

 vesicle of the brain (in a way not fully explained) till it reaches 

 the summit of the crista, which has become in the meantime 

 established. 



The auditory organ of the simple Ascidians can hardly be 

 brought into relation with that of the other Chordata, and has 

 most probably been evolved within the Tunicate phylum. 



BIBLIOGRAPHY. 



Invertebrata. 



(384) V. Hensen. "Studien lib. d. Gehbrorgan d. Decapoden." Zeil.f. wiss. 

 Zool., Vol. xin. 1863. 



(385) O. and R. Her twig. Das Nervensystem u. d. Sinnesorgane d. Medusen. 

 Leipzig, 1878. 



Vertebrata. 



(386) A. Boettcher. " Bau u. Entwicklung d. Schnecke." Denkschriften d. 

 kaiserl. Leap. Carol. Akad. d. Wissenschaft., Vol. XXXV. 



(387) C. H asse. Die vergleich. Morphologien. Histologied. hiiutigen Gehb'rorgane 

 d. Wirbelthiere. Leipzig, 1873. 



(388) V. Hensen. "Zur Morphologic d. Schnecke." Zeit. f. wiss. Zool., Vol. 

 XIII. 1863. 



(389) E. Huschke. "Ueb. d. erste Bildungsgeschichte d. Auges u. Ohres beim 

 bebriiteten Kiichlein." Isis -von Oken, 1831, and Meckel's Archiv, Vol. vi. 



(390) Reissner. De Auris internee formatione. Inaug. Diss. Dorpat, 1851. 



Accessory parts of Vertebrate Ear. 



(391) David Hunt. "A comparative sketch of the development of the ear and 

 eye in the Pig." Transactions of the International Otological Congress, 1876. 



(392) W. Moldenhauer. "Zur Entwick. d. mittleren u. ausseren Ohres." 

 Morphol. Jahrbuch, Vol. ill. 1877. 



(393) V. Urbantschitsch. " Ueb. d. erste Anlage d. Mittelohres u. d. Trom- 

 melfelles." Mittheil. a. d. embryol. Instit. Wien, Heft I. 1877. 



Olfactory organ. 



Amongst the Invertebrata numerous sense organs have been 

 described under the title of olfactory organs. In aquatic animals 

 they often have the form of ciliated pits or grooves, while in the 

 Insects and Crustacea delicate hairs and other structures present 

 on the antennae are usually believed to be organs of smell. Our 

 knowledge of all these organs is however so vague that it 



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