80 H. L. Bruner 



The Choanal Valve of Larval Amphibians. 



The choanal opening of the Amblystoma larva has been studied 

 in an incidental way by Wagler (1830, p. 316) and Calori (1851), 

 the former describiug two so-called choanal valves while the latter 

 recognized but one. In my own preparations I find a Single valve 

 which resembles in all essential particulars the choanal valve of Nec- 

 iurus. In a larval Amblystoma 14 mm. long the valve is already 

 recognizable as a slight fold on the median side of the almost cir- 

 cular opening. It evidently reaches a functional condition very early 

 in larval life. In Salamandra maculosa it seems to be fully formed 

 at birth, the larva having a length of about 25 mm. at this time. In 

 Triton alpestris the valve seems to be functional in a larva of 18.5 mm. 

 and it persists in all later stages examined, includiog a specimen 

 31 mm. long. In the large larvae of Amblystoma tigrinum the valve has 

 been observed in specimens varying from 80 mm. to 240 mm. in length. 



My material does not cover the last stages of larval life. It is 

 certain, however, that the choanal valve is a temporary structure 

 which disappears during the metamorphosis when the choana assumes 

 the peculiar form which is characteristic of the adult. During the 

 later larval stages, and before the choanal valve is lost, a new 

 mechanism for closing and opening the nasal passage makes ist 

 appearance at the external naris. This is the smooth muscle mechanism 

 of the adult Salamander. The development of this mechanism, which 

 includes a constrictor muscle and one or two dilatators, has been 

 described in a former paper (Bruner, 1901, p. 328). Early stages 

 of development occur in a larva of Triton alpestris 22 mm. long and 

 the muscles are apparently functional in a specimen of 31 mm., which 

 however still retains all of the larval characteristics. In later larval 

 life, therefore, the Salamander is provided with two mechanisms for 

 closing the nasal passage. 



In the preceding account I have mentioned only the larvae of 

 lungbearing forms. In the lungless Spelerpes ruber, Desmognathus 

 fusca and Salamandrina perspicillata a choanal valve of the type 

 described above is wanting in the larva but the choana is probably 

 closed in some as yet undiscovered way. In Spelerpes ruber regulär 

 acquatic respiration occurs, water entering the external naris and 

 passing out through the gill clefts, as observed in Neeturus. 



The choana of the frog larva is closed by a so-called choanal 

 fringe similar to that which Schulze (1892, p. 58) found in the 

 larva of Pelobates. In the bullfrog larva this fringe is a prominent 



