ip AYERS. [Vol. VI. 



According to Hoffmann and Rauber, the anterior portion of the nucleus of the 

 IX nerve, i.e. the very anterior end of the glossopharyngeus nucleus, is regarded by 

 Duval and others as the nucleus of origin of the chorda tympani and of the portio 

 intermedia Wrisbergii of the auditory nerve; however, the mass of evidence seems to 

 favor the view of a closer connection with the anterior root and the facial than with 

 the posterior root and the glossopharyngeal. 



C. Sense Organs. 



Development in Amia according to AUis. 



Development in Elasmobranchs in connection with the ear organ. 

 Development in bony Fishes. 

 Development in Amphibia. 

 Development in the Sauropsida and Mammalia. 



Views previously held of the function of these sense organs and of their 

 relation to the ear, both analogical and homological. 



The Development of the Sense Organs in Amia. 



A knowledge of the development of the lateral line sense 

 organs {e.g. as it has been worked out in Ganoids) enables us to 

 understand the development of the internal ear, and is abso- 

 lutely essential to such understanding. I give the account of 

 the development of these superficial organs in Amia in Allis's 

 own words. He says {loc. cit. p. 523 etseq.): "The inclosing 

 of the lateral canals and the formation of the ninety-three nor- 

 mal primary pores and tubes is essentially a simple and regular 

 process, but in most parts of the head marked abbreviations 

 take place, which greatly obscure it. Where the process is 

 regularly and fitlly caiTied ont, the canals arise in separate sec- 

 tions, each of zvJiich contains a single sense organ, and Jience 

 corresponds to the part between two primary tubes in the devel- 

 oped canal [italics mine]. 



" In young Amia, in which the canals have not yet begun to 

 develop, the organs of the lateral system, still below the surface, 

 appear as whitish spots, with indistinct outlines, strung along 

 more or less continuous whitish lines. These lines mark gen- 

 eral and extensive surface depressions. After a developing 

 canal organ has reached the surface at the bottom of one of these 

 depressions, it begins to sink, canying zvith it the surrounding 

 tissues, thus forming a small pit, at the bottom of which the 

 organ lies [italics mine]. A series of changes now begin, which, 

 on an exaggerated scale, are a repetition of those which lead to 



