animals to respire air without ribs or diaphragm, and without the power possessed by the tortoises and frogs to cause it to enter by the nostrils, in order that, so to speak, it might be swallowed, because the nostrils of the Sirens do not lead into the mouth, and the branchial apertures must let it escape. But his own observations, made upon well-preserved individuals, showed Cuvier that the nostrils in the Siren do communicate with the mouth by a hole pierced as in the Proteus, between the lip and the palatal bone which carries the teeth. The membranous opercula of their branchiæ are muscular internally, and capable of hermetically sealing the apertures; then it is very easy for the Siren, by dilating its throat, to introduce the air into the mouth, and to force it afterwards, by contracting the throat, into its larynx. Even without this structure of the nostrils, the animal could produce the same effect by opening its lips a little: a theory which Cuvier applies to the Proteus as well as the Siren.
Professor Owen has contributed some interesting observations to the Penny Cyclopædia,[1] on the size of the blood-disks (commonly called globules) in the Amphibia as compared with other animals. Their size in these Reptiles is very great, and their magnitude seems to bear a proportion to the permanency of the external gills, or branchiæ. In the double-breathing animals before us, the Sirens and Protei, these disks are so large as to be distinguishable even with the unassisted eye, while their appearance under a microscope is exhibited in the accompanying
- ↑ Vol. xxii. p. 61.
