226 BY THE DEEP SEA. 



the prevailing tint, but there are delicate mottlings and streaks 

 of many colours upon it. 



We now reach what we may very fitly term the Sea-slugs, 

 for they are creatures that externally have considerable resem- 

 blance to the land-slugs, though structurally they are very differ- 

 ent, and they are far removed from each other in classification. 

 The land-slugs (Limax) carry a little shell embedded in their 

 back, and their breathing organs are internal ; the Sea-slugs are 

 entirely shell-less, except in the embryo-stage, and their 

 breathing apparatus is always exposed, and situated on the 

 back or sides. In consequence of this characteristic, the Sea- 

 slugs, as a group or section of the Gasteropods, are called 

 the Nudibranchiata, or naked-gilled mollusca. They are 

 plentiful on rocky coasts, where they range from half-tide to 



SEA LEMON. 



a great depth. The best plan is to seek for them at low 

 spring-tides, turning over stones at the edge of the laminarian 

 zone, when the slugs will be found at rest on the under 

 surfaces, in a more or less collapsed condition. They will 

 readily respond, however, to the attention paid them by put- 

 ting them in the calm clear water of our collecting bottles, and 

 extending their tentacles and branchial plumes, will explore 

 their new quarters. One of the most striking of these sea- 



