148 LIVERPOOL BIOLOGICAL SOCIETY. 



or in Aplysia (fig. 2,) in a well developed state, and a trans- 

 verse section through the latter mollusc at about the 

 junction of the anterior and middle thirds of the body 

 shows that the epipodia are folds of the lateral integument, 

 extending upwards and inwards (PL VI. fig. 3, e.p.) so 

 as to cover over the greater part of the dorsal surface. 



It is generally beheved * that the fold of integument 

 over-hanging the foot in Doris should be regarded not as a 

 mantle edge but as an epipodial ridge. Figures 4 and 5 

 show transverse sections through Doris pilosa, and the 

 lateral ridges {e:p.) above the foot are seen to be large, to 

 have the same general relations as the epipodial folds of 

 Aphjsia, and to bear on their surface a number of prominent 

 papillae. When we examine next a transverse section of 

 Goniodoris nodosa (PI. VI. fig. 6) we find that the lateral 

 ridges have assumed a more dorsal position, and have 

 slightly projecting nodules or papillae at intervals along 

 their course. In Poh/cera (PL VI. figs. 7, 8, 9) we find 

 the same lateral ridge has become more prominent, bears 

 more distinct papillae throughout its course, and rises up 

 at its posterior end alongside the median dorsal branchiae 

 to form a pair or more of large simple or bifurcating 

 processes which are entitled to the name of cerata 

 (PL VI. fig. 9).f 



In the genus Idalia a similar epipodial ridge is present 

 bearing numerous slender cerata, especially in its posterior 

 part, alongside the branchiae ; and even in ^^Egirus punc- 

 tilucens, where the back and sides of the body bear 

 numerous tubercles, there is a row of larger projections 

 distinctly visible on each side, which probably represents 

 the epipodial ridge of other forms (PL VI. fig. 11, e.p.). 



* E.g., see Lankester, Ency. Brit., 9th ed., vol. xvi., Art. IMollusca, ]). 655. 

 + Pai'ieto-cerata, Herdiiiaii, loc. cit.. (^)uait. Jour. Mic. Sc, p. 42. 



