INNERVATION OF CERATA OF SOME NUDIBRANCHIATA. 545 
condition, and working up to those in which they are more 
complicated. 
POLYCERA. 
In Polycera quadrilineata the cerebral and pleural 
ganglia are completely fused to form a cerebro-pleural mass on 
each side, of which the anterior part is cerebral and the poste- 
rior pleural. The “ epipodial”’! nerves are found arising, one 
on each side, from the ventral and posterior part of this mass 
(Pl. XXXII, fig. 2, ep. .), i. e. distinctly from the pleural 
ganglia ; and they eventually run along the sides of the back 
to supply the ceratal lobed ridges found in this species. 
In one of our series we have a specimen cut into 300 sections, 
and we find, on the right side of the body, the epipodial nerve 
arising, as above described, in the 91st section, in the region of 
the reproductive aperture (see Pl. XXXII, fig. 2), and then 
running forwards? through ten sections to the 81st, in the 
region of the eyes (Pl. XXXII, fig. 1, ep. m.), where it sud- 
denly bends round ventrally, and can then be traced back wards 
through the same series of sections (81 to 91). 
In the 90th and 91st sections (Pl. XXXII, fig. 2) the cut 
end of the nerve is seen lying dorsally and externally to 
the point of origin from the ganglion, but free in the body- 
cavity. It can be traced back in this same free condition to 
about the 120th section, when it sinks gradually into the meso- 
dermal body-wall. The nerve then continues to pass back- 
wards in a dorso-lateral position, lying just over the lateral edge 
of the ovo-testis, which overlies the liver in this part of the 
body (Pl. XXXII, fig. 3, 0. ¢.). In about the 160th section the 
ceratal (epipodial ?) ridges begin to be more prominent, and a 
few sections further on (No. 165) a branch is seen arising from 
1 Throughout the present paper we shall continue, in the anatomical 
descriptions, to call these nerves epipodial, without considering now the 
question of whether the parts they supply are to be regarded as “ epipodial,” 
* pleuropodial,” or not “ podial” at all. 
? Possibly in consequence of the retracted position of the nerve collar, due 
to contraction of the animal at death. 
