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 wliole 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 woi'ds of Cuvier when speaking of the Siren, 

 " J'ai sous les yeux les poumons ou I'appareil vasculaire est aussi developp6 

 et aussi compliqu6 que dans aucune reptile." Nevertheless we cannot call 

 it strictly 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) possesses a single undivided auricle : and were even the ' septum auri- 

 cularum' absent in the Salamander or Frog, these would not, therefore, be 

 Fishes. 



Neither can we call the Lepidosiren a Fish, simply on account of its having 

 branchial arches and gills, inclosed in a branchial chamber, with a single 



