INNERVATION OF CERATA OF SOME NUDIBRANCHIATA. 550 
their possessors ; and it may readily be imagined that when 
such modifications have taken place as led to the appropriation 
of important organs like large blood-sinuses, huge hepatic ceca, 
and cnidophorous sacs, it would not be unlikely for nerves in 
the neighbourhood to be diverted from their original positions 
and become drawn up into the cerata. 
The condition of Facelina, where there is what may be the 
commencement of a pleural supply, and in Dendronotus,. 
where the anastomosis may be the remains of an original pedal 
supply, suggest at least the possibility of the following as an 
explanation ; viz. (1) that these ceratal outgrowths may be truly 
epipodial, homologous with the epipodia of Trochus, starting 
at first as pedal structures supplied with nerves from the pedal 
ganglia ; and (2) may have secondarily acquired, possibly as the 
result of changes in form, position, and relations to other 
organs, a supplementary nerve-supply from the adjacent in- 
tegumentary nerves arising from the pleural ganglia; and (3) this 
supplementary supply, while remaining subordinate in Face- 
lina, may in other forms have gradually come to supplant the 
original epipodial (pedal) nerves, which (on this view) have now 
completely disappeared in such forms as Polycera and 
Ancula, and are only represented in Dendronotus by the 
pleuro-pedal anastomosis. This is, however, only a suggestion, 
which we do not feel able to support or press further at present. 
We may possibly be able to get evidence for or against it from 
the examination of the nerve-supply in some additional forms 
of Nudibranchs, which we hope soon to undertake. 
If, then, the cerata of Nudibranchs cannot all be said to be 
true epipodia innervated by the pedals, we have shown, at 
least, (1) that it is equally impossible to regard them all as 
pallial outgrowths supplied by the pleural ganglia, and (2) 
that possibly they may have been epipodial in origin, although 
there is now in some a connection with pleural nerves. 
