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, ep.) so 
as to cover over the greater part of the dorsal surface. 
It is generally believed * 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 
Aplysia, and to bear on their surface a number of prominent 
papille. When we examine next a transverse section of 
Gontodoris nodosa (Pl. VI. fig. 6) we find that the lateral 
ridges have assumed a more dorsal position, and have 
shehtly projecting nodules or papille at intervals along 
their course. In Polycera (Pl. VI. figs. 7, 8, 9) we find 
the same lateral ridge has become more prominent, bears 
more distinct papillze throughout its course, and rises up 
at its posterior end alongside the median dorsal branchiee 
to form a pair or more of large simple or bifurcating 
processes which are entitled to the name of cerata 
GEG WAL, 1ve2, Qa) 
In the genus /dalia a similar epipodial ridge is present 
bearing numerous slender cerata, especially in its posterior 
part, alongside the branchiz; and even in 4girus 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. Mollusca, p. 655. 
+ Parieto-cerata, Herdman, loc. cit.. Quart. Jour. Mic. Se., p. 42. 
