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 vertebræ, 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 vertebrz by opposite concave facets. Now the Perenni- 
branchiate Bafrachia do in faet present this very structure; yet they have 
not, any more than the Jchthyosauri, 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 tbe scaly nor naked reptiles has the skeleton been found to 
VOL, XVIII. . A ; 
