350 Prof. Owen’s Description of the Lepidosiren annectens. 
form of the ovaria and the convoluted disposition of the oviduct resemble 
more the same parts in the Axolotl, Amphiuma and Siren. 
Concluding Observations. 
Most naturalists have considered the Vertebrate animals to form four di- 
stinct classes, characterized by as many leading modifications of the respira- 
tory organs; Mammals, e. g., being distinguished by having lungs composed 
throughout of a dense spongy texture, and suspended freely in a thoracic ca- 
vity; Birds, by having spongy lungs firmly adherent to the posterior parietes 
of the thorax, and generally communicating with air-cells continued into the 
abdomen and other parts of the body ; Reptiles, by membranous lungs extend- 
ing into the abdominal cavity ; and Fishes, by breathing with gills alone. 
It is true, that the limits which separated the two classes of cold-blooded 
Vertebrates were overpassed by the Batrachian Reptiles, which possess gills 
during either a part or the whole of their existence ; but as lungs of the 
Reptilian type coexisted with these gills in the mature animal, these have 
been always separated from Fishes, either as an order of Reptiles, or as a di 
stinct class, under the name of Amphibia. Their air-breathing organs were, 
in fact, regarded as such essential indications of their superiority to Fishes, 
that when the heart of the Batrachia was believed to be diccelous, and before 
it had been demonstrated that the most fish-like of the Amphibia, as the Siren, 
had a double auricle, they were equally regarded either as a class or sub-class 
of Reptiles. 
In the Lepidosiren, however, we have a cold-blooded vertebrate animal, of 
which I may say in the very words of Cuvier when speaking of the Siren, 
Jai sous les yeux les poumons ou l'appareil 
et aussi compliqué que dans aucune reptile.” Nevertheless we cannot call 
it prety and zoologically a Batrachian ; not, however, because the heart 
has one instead of two auricles, for one, at least, of the Amphibia (the Pro- 
teus 1 Tv L s 
) possesses a single undivided auricle: and were even the ‘septum auri- 
wont absent in the Salamander or Fro these would not, therefore, be 
ishes. 
vasculaire est aussi développé 
Neither can we call the 
Lepidosiren a Fish, simpl ; s 
branchial arches and gi ply on account of its having 
Ils, inclosed in a branchial chamber, with a single 
