ALIMENTARY CANAL IN LEPIDOSIREN AND PROTOPTERUS. 509 
believed that the arrangement in Lung-fishes had actually 
come about in this way, and that in Actinopterygians matters 
had gone a step farther in that the glottis had become dorsal 
as well as the lung itself. Sagemehl, it is true, greatly 
impressed by the discovery that in Ery thrinus, Macrodon, 
and Lebiasina the glottis was situated on the left side of 
the pharynx, took the view that in the Actinopterygians the 
migration of lung apparatus had been up the left side of the 
pharynx instead of up the right side, as in Lung-fishes. No 
one, however, who is familiar with the wide range of variation 
in the position of the glottis, now to the right, now to the left 
side of the median plane in e. g. Characinids and Siluroids^ 
will probably see any reason to suppose that the lung migra- 
tion has not taken place in exactly the same fashion in the 
Actinopterygians and in the Lung-fishes. 
The Lung of Polyp ter us. — The condition of the lung 
in the adult Polypterus (text-fig. 11, a) must be noticed, 
especially in regard to three points. Firstly, the lung is here 
an important hydrostatic organ, and correlated with this we 
find that the lung apparatus as a whole shows a symmetrical 
arrangement. The hinder half of the large right lung being 
without any fellow on the left side to balance it, has assumed 
a median position lying in the dorsal mesentery, and is prac- 
tically symmetrical about the mesial plane; " it is only in its 
anterior half, where it is still balanced by the remains of the 
left lung, that it bends away from the mesial plane towards 
the right. It is obvious then that, were the left lung to 
undergo still further reduction, we should expect more and 
more of the right lung to assume the mesial position, until at 
last, when the left lobe had approached vanishing point, the 
right lobe would tend to be symmetrical about the mesial 
plane right to its front end. The whole lung apparatus 
’ More especially if we Lear in mind the fact, chronicled above, of the 
definitely dorsal side of the lung in the young lung-fish being carried 
temiiorarily to the left side by the primary torsion. 
- In the dissection shown in text-fig. 11 a the hinder i)art of the right 
lung has been displaced towards the right side and the symmetry is 
consequently destroyed. 
