MOVEMENTS OF NECTURUS AN U CRYPXOBKANOllUS. (i5] 



by him in XectiirtijS does not include tiie gross flapping of the ex- 

 ternal gills. There is, therefore, an a[)parent textual discrepancy 

 between his account and mine, which will doubtless be cleared by 

 further independent observations, Bruner fortilies his statements 

 concerning the " bucco-pharyngeal mechanism " by a carefid 

 description of the choanal valve of ^Yecturus ; and he seems to 

 assign a preponderating role to the gill-clefts in the branchial 

 resjiiration of this genus. It is not altogether inconceivable that 

 in difl'erent parts of its climatic range, as well as under diverse 

 laboratory conditions, the sevei'al components of the respiratory 

 tract may vary in the relative frequency of their turns. 1'he 

 behaviour of Cri/ptobranckus informs us that not every yawn is 

 an act of breathing. No contrast could be more realistic than 

 that between the restless, air-ciuving CryjAohranchus and the 

 listless, gill-waving Necturus \\\\q\\ viewed at the right biological 

 moment in the splendidly appointed tanks of the New York 

 Aquarium. 



McGill Universitj', Montreal, 

 October 10, 1920. 



