161 



BIOLOGY. 



[Book ti. 



eadstitig in the inferior animals, — ^are also found on the buccal 

 orifice, in form of a cupping-glass, of the cyclostbmes. The 

 amphibians have likewise analogous organs on the edge of their 

 jaws. 



In the fishes, the ganoids and the teleostians, there are teeth on 

 the jaws, the paleital bones, the vomer, the hyoid bone and the 

 bronchial arcs ; the seUxdans have none except on the jaws.. 

 (Kg. 10.) 



A 



Fio. 9. 

 Digestive tube of fishes. A, gobius meUna. 

 stomus. B, salmon.- o, oesophagus ; v, sto- 

 maoh; », mediin infestW: <««. BTloric 

 appendices ; r, rectum. 



Fio. 10. 

 Bneoal opening of the yefro- 

 im,yzon marvnms, with corneoua 

 t^eth. 



The teeth of fishes, of ampHbians, of reptiles fall and are 

 renewed during the whole of life. 



The three divisions of the digestive tube, properly so called, 

 grow gradually more perfect in proportion as the animal rises in 

 the hierarchy of the vertebrates. 



In fishes the first part of the digestive tube has direct 

 continuity to the stomach without difference of diameter (Kg. 9). 



