352 Prof. Owen's Description of the Lepidosiren annectens. 



present this colour: yet it is almost superfluous to remark that so trivial a 

 character would of itself have been totally inadequate to determine the classific 

 characters of a doubtful species : it is only in conjunction with other modi- 

 fications of structure that it assists in our present attempt to determine the 

 true affinities of the Lepidosiren. 



As regards the principal conditions of the organs of generation, the line of 

 demarcation cannot be drawn between the Amphibia and the Plagiostomous 

 Chondropterygii : and the structure of these organs in the Lepidosiren, while it 

 shows its near affinity to the Reptiles, by no means proves that it is not a Fish. 



The brain of the Lepidosiren like its generative system indicates its close 

 relationship as a Fish with the Amphibia, but nothing more. 



The optic nerves do not decussate, but come off^ from nearly the same point 

 in front of the infundibulum : since, however, the same structure exists in the 

 Sharks and Rays, this likewise fails to establish the amphibious character of 

 the Lepidosiren. 



On the other hand, the simple condition of the organ of hearing, consist- 

 ing merely of the labyrinth without a cochlea, or a fenestra rotunda, might 

 be taken as proof of the ichthyic nature of the Lepidosiren: the organ of 

 hearing, however, presents, as is well known, a similar simple condition in the 

 Perennibranchiate Reptiles. 



In the organ of smell we have, at last, a character which is absolute in 

 reference to the distinction of Fishes from Reptiles. In every Fish it is a 

 shut sac communicating only with the external surface ; in every Reptile it is 

 a canal with both an external and an internal opening. 



According to this test, the Lepidosiren is a Fish : by its nose it is known not 

 to be a Reptile : in other words, it may be said that the Lepidosiren is proved 

 to be a Fish, not by its gills, not by its air-bladders, not by its spiral intestine, 

 not by its unossified skeleton, not by its generative apparatus, nor its extre- 

 mities, nor its skin, nor its eyes, nor its ears, but simply by its nose ; so that 

 at the close of our analysis we arrive at this very unexpected result, that a 

 Reptile is not characterized by its lungs nor a Fish by its gills, but that the 

 only unexceptionable distinction is afforded by the organ of smell. 



The anatomical facts already detailed fully justify this emphatic summary 

 of the evidence deducible from the dissection of the Lepidosiren ; yet it must 



