102 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



which are shown in fig. XX. No. 1 is the large yellow 

 sea-lemon (Archidoris tuherculata) frequently found in 

 rock pools during the spring and summer ; 2 is the rarer 

 and smaller Polycera quadrilineata, marked with yellow 

 spots and found sometimes creeping on the blades of 

 Laminaria; 3 is Eolis tricolor, one of the most graceful 

 and brilliantly coloured of the sea-slugs ; and 4 is the 

 little Doto coronata found on colonies of Zoophytes, upon 

 which it feeds. The brightly-coloured projections on the 

 back of Eolis have batteries of microscopic stinging 



Fig. XX. 



threads which can be discharged instantaneously into any 

 offending animal. Those sea-slugs which have no sting- 

 ing organs are for the most part coloured and shaped so as 

 to closely resemble their natural surroundings, and so 

 escape the observation of their enemies, while those (like 

 Eolis) with offensive organs are conspicuous and bril- 

 liantly coloured, as if to warn other animals to avoid 

 them. In losing the shell these Molluscs have lost a pro- 



