346 PHILOSOPHY OF ZOOLOGY. 



issue a multitude of fleshy leaves, or fringed vascular fi- 

 brils, resembling plumes, and closely connected at the base. 

 These are of a red colour in almost all fishes in a healthy 

 state. The internal or convex side of the support next the 

 mouth exhibits many singular differences. It is always 

 more or less furnished with tubercles. These, in the genus 

 Cyprinus, are smooth, in the Cottus rough. They are 

 lengthened into slender spines in the herring and smelt, 

 but in the former these are serrated, while in the latter they 

 are smooth. This concave part of the gill is of a white 

 colour, and forms a striking contrast with the colour of the 

 convex side. 



In some osseous fishes, the gills exceed four in number 

 on each. In the herring, for example, there is a small im- 

 perfect gill on each side, attached to the inner side of the 

 gill-lid, on which all its motions depend. It has no bony 

 arch nor concave side. At the entrance to the gullet there 

 is a cartilage on each side, studded with tubercles, resem- 

 bling, in appearance, the concave side of the last gill, but 

 connected with deglutition. In the plaise, a similar gill 

 may be observed on the inside of the gill-lid, but no dis- 

 tinct appearance of a sixth gill at the entrance to the oeso- 

 phagus. 



In the chondropterygii, the gills are far from being so 

 perfect. They are fixed to partitions which serve the pur- 

 poses of the bony arches in the osseous fishes. These par- 

 titions extend from the mouth to the gill-opening, and vary 

 in number according to the genera. They are destitute of 

 the inner or concave white side, but the fleshy leaflets are 

 of the same structure with those on the convex part of the 

 gills in osseous fishes *. 



* We are indebted to that distinguished anatomist, Sir EVERARD HOME, for 

 some important observations on the respiratory organs of the lamprey and 



