64 H. L. Bruner 



and after a thorough anatomical study of these and allied forms, 

 confirmed Cuvier's view in regard to the general character of the 

 mechanism employed in pulmonary respiration. His conclusions 

 differed from these of Cüvieb in one respect, however: he located 

 the apparatus for closing the nasal passage at the choana, whereas 

 Cüvier placed it at the external naris. By the use of modern methods 

 Mrs. Wilder (1909) has shown that the nasal vestibule of Amphiuma 

 and Cryptobranchus is provided with smooth muscles, apparently 

 homologous with those of the higher urodeles, while Anton has ob- 

 served choanal valves in Necturus, Proteus and Siren. Other questions, 

 concerning the nature and function of the choanal valves, concerning 

 the closing of the mouth and gill clefts, also in regard to the sequence 

 of events in pulmonary respiration, have not yet been answered in 

 a satisfactory way. 



From the foregoing review it seems desirable that the respiratory 

 mechanism of the lower urodeles should be more carefully studied 

 and compared with that of higher amphibians. Since the lower 

 urodeles resemble in many respects the larvae of higher amphibians, 

 the latter should also be included in the investigation. 



This paper is the result of studies carried on during the aca- 

 demic year 1910 — 1911 at the University of Pennsylvania, where 

 the author held a Fellowship for Research on the George Leib Harrison 

 Foundation. 



Physiological Observations. 

 Acquatic Respiration. 



In amphibians with gill clefts the bucco-pharyngeal mechanism 

 of pulmonary respiration is used also in afcquatic respiration. 



In Neeturus and the larvae of higher urodeles {Amblystoma) 

 regulär oscillations of the floor of the mouth occur, elevation being 

 brief and conspicuous while depression is so slow that it may easily 

 be overlooked. During the period of depression the mouth and gill 

 clefts are usually closed and water enters only through the nasal 

 cavity. During the period of elevation water is forced out usually 

 through the gill clefts, sometimes between the lips, not through the 

 nasal cavity. 



Siren, Amphiuma and Cryptobranchus allegheniensis have regulär 

 bucco-pharyngeal movements similar to those of Neeturus, water 

 entering usually through the nostrils and passing out through the 



