﻿174 Proceedings of the Royal Physical Society. 



assuming that a rotation of the lung rudiment (in a counter 

 clock-wise direction, as seen from the tailward direction) 

 took place as the lung became shifted dorsalwards, and 

 before the secondary nervous connection with the left vagus 

 became developed. 



In regard to the Teleostean Fishes, it seems probable that 

 the condition of their swim-bladder is to be looked upon as 

 representing a further stage in the same evolutionary process 

 as has taken place in Oeratoclus. In them the swim-bladder 

 has become single and dorsal, and a shortening of the 

 pneumatic duct has led to the glottis also becoming dorsal 

 in position. It seems unwise, in the present state of our 

 knowledge, to look upon the departures from the mid-dorsal 

 position of the glottis found in various Teleosts {e.g., towards 

 the right in Siluroids, towards the left in Characinids) as 

 variations of any special phylogenetic importance. The 

 features of the Teleostomi generally are such as to make 

 it probable that they are descended from Crossopterygian- 

 like ancestors, and that in their case also, owing to the 

 enlargement of the right lung in these ancestors, the swim- 

 bladder has migrated round the right side of the gat. The 

 condition in Erythrinus, where the glottis is on the left side, 

 about mid-way between dorsal and ventral sides, would still 

 be of interest as showing the instability of the mid-dorsal 

 position of the glottis, but woul'd not be looked upon as 

 representing a phyletic stage in the dorsalward migration of 

 the glottis, as Sagemehl believed.^ 



^ In this dorsalward migration of the glottis, probably torsion of the 

 oesophagus about its longitudinal axis has played an important part. 

 Cf. Moser, Arch. mikr. Anat., 1904. 



