SEA-SNAILS AND SEA-SLUGS. 227 



slugs is the Sea Lemon (Doris tuberculatd), which is about 

 three inches in length, broad, and with the upper surface 

 thickly studded with tubercules ; this, in conjunction with 

 its colour, gives it a very close likeness to the half of a 

 lemon adhering to the rocks. As will be seen in the illustra- 

 tion, there are two tentacles, and these are retractile within 

 special cavities. The branchial plumes are arranged in a 

 crown-like circle in the middle of the back, but near to the 

 posterior end ; and these also can be withdrawn at the crea- 

 ture's will. There are several British species, some of them 

 very small, and they range from low-water to twenty-five 

 fathoms, feeding upon zoophytes, sponges, anemones, and 

 their own kind. 



Doris johnstoni is a smaller species than tuberculata^ but is 

 worthy of attention on account of a certain resemblance to 

 Lamellaria. It is " got up " to mimic a sponge. There are 

 no tubercles on its surface, which is very finely roughed, so 

 that it is sponge-like to the touch. In colour it is creamy, 

 wonderfully speckled with larger and smaller spots of pale 

 brown, that produce the effect of the porous surface of a 

 sponge, and the large spots are touched up with a darker 

 brown, to give depth to these false pores. When it is explained 

 that D. johnstoni feeds on sponges like Halichondria panicea, 

 this colouring is easily understood, but its marvellous nature is 

 not lessened. 



Some species of allied genera are quite remarkable, one 

 might almost say eccentric, in their ornamentation. dZgirus 

 punctilucens, a species found between tide-marks, is elabo- 

 rately covered with large tubercles and shining points ; the 

 branchial tufts assuming quite a tree-like growth in miniature, 

 around the orifice, which is placed further forward than in 

 Doris. 



The Crowned Eolis (Eolis coronatd) has a slender body, 

 long slender tentacles, that cannot be withdrawn, and the 

 back is covered with long papillae, gathered into a dozen 



