354 Prof. Owzw's Description of the Lepidosiren annectens. 
M. Agassiz has confirmed this statement, and further observes, that the 
ductus pneumaticus communicates with the pharynx by a large and regular 
slit, which he regards * as bearing even a closer resemblance to the entrance 
of the trachea of the Pulmoniferous Vertebrata in general, than the aperture 
by means of which the lungs communicate with the pharynx in the Perenni- 
branchiate Amphibia*.” In the Polypterus, lastly, we find an approach to 
the Lepidosiren in the air-bladder being double, consisting of two long cylin- 
drical lobes, but of unequal length, the left being the longest, and extending 
through the whole length of the abdomen: the communication of the trachea, 
or ductus pneumaticus, with the cesophagus, is also here described by Geoffroy 
St. Hilaire as consisting of a fissure provided with a constrictor muscle. 
. The Polypterus, moreover, presents a most interesting trait of affinity to the 
Lepidosiren in the shortness and straightness of its intestinal canal, which is 
provided with an internal spiral valve. 
With these advances in the organization of the air-bladder in certain abdo- 
minal Fishes towards the reptilian structure of the lung, made by the Amia 
and Lepidosteus on the one part, in the cellular complication of a single cylin- 
drical air-bladder; and by the Polypterus, on the other hand, in the division 
of the air-bladder into two lobes, with the slit-shaped glottis of the ductus 
pneumaticus described by Geoffroy and Agassiz ; there wanted only the com- 
bination of the three characters, as it occurs in the Lepidosiren, of a double 
as well as cellular air-bladder, with a rudimental larynx, to dissipate the last 
doubts entertained by the stanchest realist as to the true homology, long ago 
pointed out by Harvey and Hunter, of the vesica natatoria and ductus pneu- 
maticus of the ichthyologist. 
Having indicated some of the affinities of the Lepidosiren, considered as a 
Fish, to certain species of the Sauroid family, I may further observe, that in 
the helmet-like plate into which a part of the frontal is developed, we perceive 
- —À to the genus Heterobranchus amongst the Siluroid family of 
abdominal soft-finned Fishes, most of the species of which also possess a 
bilobed air-bladder communicating with the cesophagus 
pancreatic cæca. 
When we consider also that the Esocide have alla large air-bladder 
and are deficient in 
and 
* Zoological Proceedings, 1834, p. 119. 
