354 MARINE INVERTEBRATES 
in most nudibranchs is extremely large and completely surrounds the 
stomach, in Dendronotus also extends into these dorsal cerata, so that 
they may have some sort of digestive function. 
Dendronotus arborescens. 
Genus Molis 
ZE. papillosa. This is probably the commonest nudibranch upon 
the North Atlantic coast, and it occurs as frequently in European 
waters. It may readily be found clinging to stones, alge, the piling of 
wharves, eel-grass, etc., in bays or in rocky tide-pools.e The color is 
yellowish-gray to orange, with purplish or olive 
spots. The cerata are very numerous, and cover the 
dorsal portion of the animal save for an open space 
along the middle of the back. There are two sets of 
tentacles, the two dorsal and the two simple labial 
tentacles. The foot tapers behind to a sharp point, 
and is truncate in front. As in Dendronotus, the 
liver is diffused into the cerata, which in olis are 
simple tubular processes without the branching 
character of those of the former. Both species lay 
their eggs in a gelatinous, bobbin-like cord, which 
is hung in festoons over rocks or upon zodphytes, or 
at times they wind the cord in a coil upon the sur- 
faces of stones. When the young first hatch out, 
Hiolis papittosa. they are provided with a glassy nautiloid shell, a fact 
which would indicate that at some remote period they 
were, like most mollusks, provided with a shell. -olis swims in an in- 
verted position, and isat times exceedingly active. It is very variable in 
coloring and in the number of cerata. 
Genus Doris 
D. bilamellata. In Doris we find a quite different type of nudi- 
branch from that presented by the two genera Dendronotus and olis. 
In one there were numerous branched cerata or dorsal papille, in the 
other many plain cerata, and in neither case were there any specialized 
