THE SEA-SLUGS. 251 



half-dozen species, it is not necessary for us to name these 

 new genera. 



The first species is very large, and is common in most 

 places far out on the rocks. If at a low spring tide you go 

 far out on the rocks and look carefully down the narrow 

 clefts, you will probably see large weird creatures, yellowish 

 in colour, soft to the touch, and shapeless in appearance. 

 They often reach a length of over three inches, and are 

 broad and massive. If you can successfully extricate them 

 from the rock crevices, place your specimens in water and 

 watch them unfold. There is no trace of shell, external or 

 internal, and the branchial plume of Aplysia has also dis- 

 appeared. The body is elliptical and depressed, and the 

 head is not separated from it ; the mantle-fold of the Azygo- 

 branchs is also absent. The dorsal surface is covered by 

 what systematists call the cloak, or mantle, which is really 

 equivalent to the epipodia of Aplysia. It is closely covered 

 with round tubercles, and is strengthened by spicules. 

 Through two little holes in it the short conical tentacles 

 are protruded anteriorly. At the other end, also on the 

 dorsal surface, is the median anus, which is surrounded by 

 a circle of feathery "gills," not homologous with the gill 

 of Aplysia. They are nine in number, are large and tri- 

 pinnately cut, or fern-like, and can be completely withdrawn 

 into the body. The foot forms a bright yellow creeping 

 surface, and is as broad as the body. The upper surface 

 in life is often bright in colour, with patches of blue-green 

 on a yellowish ground. This is Doris tuberculata, the 

 largest of our British Dorids. Like other species it lays 

 white ribbons of spawn on the rocks, but the process 

 is more easily observed in some of the more abundant 

 species. I have not found it easy to keep in confinement, 

 but there is usually no difficulty in obtaining specimens for 

 examination, especially in the earlier part of the year. 



The next species, Doris johnstoni (see- Fig. 72), is rarer, 

 but occurs occasionally between tide-marks. It is not very 

 much smaller, for it may reach a length of two inches, but 

 is readily distinguished by the different shape and the more 

 numerous gills. The body is convex in the centre and 

 markedly depressed at the sides; the dorsal surface is 

 covered with very minute tubercles, and is blotched with 



