Prof. Owen's Description of the Lepidosiren annectens. 351 



opercular outlet ; because the larva of the tailless Batrachian presents at one 

 period of its existence a similar structure ; yet if that state were persistent 

 instead of transitory, it would still be a Reptile and not a Fish. It cannot 

 therefore be determined by the modifications of the respiratory organs 

 whether the Lepidosiren be a Fish or a Reptile. Can it be proved to be a 

 Fish by the modifications of its digestive system ? A straight intestine with 

 an internal spiral valve has hitherto been met with only in the class of Fishes ; 

 yet it occurs rather as an exceptional than a general structure in that class. 

 Supposing that a spiral intestinal valve had been discovered in the Amphiuma, 

 Siren, or Proteus, should we have been justified on that ground in removing 

 such species to the class of Fishes ? There is good evidence that the intestine 

 of the Ichthyosaurus was provided with a spiral valve, yet it is not on that ac- 

 count regarded as a Fish. If I mistake not, indeed, the intestinal spiral valve 

 of higher Chondropterygii is a structure dependent on a slight modification 

 only of that peculiar disposition of the intestinal canal which characterizes 

 . the gill-breathing larvae of the Batrachia : we have but to inclose the series of 

 spiral coils of gut of the tadpole in a common investing membrane, so as to 

 conceal the complication under a simple exterior, and little more is wanting 

 to render the conversion of the one into the other structure complete. 



In reviewing the peculiarities of the osseous system with reference to the 

 affinities of the Lepidosiren, it may first be remarked, that no Amphibian has 

 hitherto presented an unossified condition of the bodies of its vertebrae, or of 

 the parts of the skull containing the organ of hearing. Would such osteolo- 

 logical modifications, it may be asked, have sufficed to alter our opinion of the 

 classific relations of the Siren ? Such a condition of the skeleton, it may be 

 answered, is by no means characteristic of the class of Fishes. If any general 

 ichthyic character can be taken from the skeleton, it is the reciprocal union 

 of the bodies of the vertebrae by opposite concave facets. Now the Perenni- 

 branchiate Batrachia do in fact present this very structure ; yet they have 

 not, any more than the Ichthyosauri, been transferred to the class of Fishes 

 on that account : we may conclude, therefore, that their position in zoological 

 classifications would not have been changed, even if their skeleton had resem- 

 bled that of the Lepidosiren. It is only in a few fishes that the bones are 

 green ; neither in the scaly nor naked reptiles has the skeleton been found tq 



VOL. xvm. 3 A 



