DORIDOBIDES GARDINERI. 291 
us to believe that the holohepatic condition is the more 
primitive, and the cladohepatic condition derived from it, 
though it may make its appearance very early in the pedigree 
of the nudibranchiata. Further, if it is admitted that a com- 
paratively unspecialised group (such as the Tritonude) con- 
nects two highly specialised groups (such as the Afolididee 
and the Dorididz), the origin of the whole series is probably 
to be sought in or near the unspecialised group, and we there- 
fore think with Pelseneer that T'ritonia,! or rather some 
extinct allied form must be the ancestor of both the Holohe- 
patica and Cladohepatica, and likewise nearly allied to the 
Tectibranchs.?, Pleurobranchea is certainly the Tecti- 
branch which most nearly resembles the Holohepatica, but it 
does not follow that it is necessarily their direct ancestor, for 
the characters of the Pleurobranchidez appear to be due to the 
shell being enclosed by the integuments, the asymmetrical 
ctenidium remaining; whereas in many nudibranchs, at any 
rate, the shell is rejected in the larval stage, not enclosed, no 
ctenidium is formed, but symmetrical respiratory organs of 
various types are developed instead. Nothing except the fact 
that the more primitive nudibranchs, as far as they are known, 
seem nearly allied to one another, renders it improbable that 
more than one type of larva may have adopted this method 
of development by rejection of the shell and symmetrical 
growth. 
Are the more primitive nudibranchs those with or those 
without special gills ? It will be well to review the principal 
gill-less forms more or less allied to l'ritonia. It may be 
premised that all the Dorididz appear to have pallial respira- 
tion (as also the Pleurobranchide) which is merely supple- 
1 Tritonia itself may have developed special features, such as its oral veil, 
tentacles, peculiar rhinophores, and branchie. 
2 This is without prejudice to the question of the derivation of the Ely- 
sioidea from the Ascoglossa. It seems to us possible that the Nudibranchiata 
(like the shell-less Pulmonata) may be polyphyletic, but that, if so, it is more 
likely that the Elysioidea have a different origin from the Adolids than that the 
Aolids have a different origin from the Dorids. But Myrrhine to some 
extent connects the Alolids and Elysioidea. 
