354 Prof. Owen'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 f^ertebrata 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 oesophagus, 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 afiinity to the 

 Lepidosiren in the shortness and straightness of its intestinal canal, which is 

 provided with an internal spiral ralve. 



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 aflinities 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 

 a resemblance 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, and are deficient in 

 pancreatic caeca. 



When we consider also that the Esocidce have all a large air-bladder, and 



* Zoological Proceedings, 1834, p. 119. 



