MARINE SNAILS. 



283 



under its inferior border on both sides of the body, or upon 



one side only, while in the Tectibranchiata they are placed, as 



in the Nudibranchiata, upon the 



dorsal aspect of the body, but are 



protected by a fold of the skin. 



In the Cyclobranchiata they form 



a fringe round the margin of the 



body, between the edge of the 



mantle and the foot, and in the 



Scutibranchiata and Pectinibran- 



chiata they are pectinated, or 



shaped like the teeth of a comb, and placed in a large hollow 



chamber, which opens externally at the side of the body or 



above the head. 



Nothing can be more elegant or various than the form and 

 arrangement of the gills in most of the nudibranchiate gastero- 



Tiara. 



Glaucus. 



Scyllsea. 



pods. In the Grlauci and Scylheae, we see at each side of the 

 elongated body long arms branching out into tufty filaments ; 

 in the Briarei a hundred furcated stems serve for the aeration 

 of the blood. On the back of the Eolides the gills are arranged 

 in rows ; in the Dorides they form a wreath or garland round 

 the posterior intestinal aperture. 



The beauty of these animals corresponds with their charming 

 mythological names, for every part of them which is not 



