160 H. L. Bruner 



prevents both air and water from entering the nasal cavity from 

 the mouth (Brunee, 1913). The organ of Jacobson begins to de- 

 velop at a very early stage in both frog and Salamander, and it has 

 been supposed (Gegenbaue, 1898) that it assumes its special func- 

 tion already in larval life. But if Setdel's theory in regard to 

 the use of this organ is correct, we must believe that it exercises 

 this function only during adult life, for the choanal valves persist 

 up to the time of the metamorphosis. 



In the larvae of lungless Salamanders (Desmognathus fusca, 

 Spelerper ruber) a ehoanal valve is wanting and the respiratory 

 medium may pass through the nasal cavity from the mouth. 



Cryptobranchus and Amphiuma resemble the higher urodeles 

 in the general structure of the nasal organ, in the form and location 

 of Jacobson's organ (Anton, 1908), and in the possession of smooth 

 muscles for opening and closing the external naris (Mrs. Wilder, 

 1909). At the choana, however, peculiar conditions occur in the 

 cryptobranchiates. The valvulär nature of the choana of Amphiuma 

 has been recognized by various authors since the time of Cuvier- 

 The valve is not a mechanical one, however, as held by Fischee 

 (1864), but is under the control of striated muscles (Beuner, 1913). 

 In Cryptobranchus allegheniensis a special choanal valve is wanting, 

 but the choana can be closed by the hyoid arch. Cryptobranchus 

 and Amphiuma are each provided, therefore, with two mechanisms for 

 closing the nasal passages. Of these, the smooth muscle mechanism 

 is used during pulmonary respiration, as is its homologue in the 

 higher urodeles. During bucco-phavyngeal respiration the choana 

 alone is closed (Bruner, 1913). 



Water is the usual medium of smell in Amphiuma and Crypto- 

 branchus. During ordinary bucco-pharyngeal respiration, water 

 enters the nostrils and passes out through the gill clefts, but its 

 return from mouth to nasal cavity is always a possibility. During 

 pulmonary respiration air passes in and out through the nasal cavity, 

 but its use for olfactory purposes is uncertain. 



Siren is provided with a well developed olfactory organ, in- 

 cluding a large organ of Jacobson which has been described by 

 Wilder (1891), Seydel (1895) and others. A closing mechanism is 

 wanting at the external naris, but a complicated choanal apparatus 

 is present, including a median valve, apparently homologous with 

 that of the larval Salamander, and a posterior valve, which is under 



