528 F. M. MacFarranD, 
opening thus formed is lined in its upper portion by high columnar 
cells, bearing very long cilia, which are directed downward. The 
kidney itself is everywhere lined with small eubical cells, each with 
a large distal vacuole. A small area of dense protoplasm surrounds 
the basally placed nucleus. The general structure of the kidney 
agrees with the descriptions given by Hecat (1896) for the Nudi- 
branch kidney. The external opening, the renal pore, is located 
immediately below the outer row of cerata on the right side, a short 
distance behind the genital opening, and but slightly behind the 
level of the renal syrinx. Externally it is a minute pore which may 
be easily overlooked. Histologically it is lined by a low eiliated 
epithelium, replacing the renal cells within, and passing over into 
the general epithelium of the body wall at the margin of the pore. 
Nervous system. The central nervous system of Dirona is of 
the general Aeolid type, and is represented for Dirona pieta in 
Fig. 24 of Pl. 32, as seen in dorsal view. The buccal ganglia have 
been removed from their natural position beneath the cerebral pair, 
where they would have been entirely concealed. 
The cerebral and pleural ganglia of each side are fused in a 
single mass, and are in close contact in the median line, being 
united in the anterior portion by a very short commissure. The 
antero-median portion of the cerebral moiety is prolonged into a 
bluntly pointed lobe, while its lateral portion is also widened out 
into lateral lobes. The pleural portion of the cerebro-pleural complex 
is more nearly spherical, as are also the pedal ganglia, which are 
closely united to the cerebro-pleural complex by the short cerebro- 
pedal and pleuro-pedal connectives. From the cerebral ganglia arise 
the following nerves, which are here designated in the same manner 
as in Fig. 24 of Pl. 32, to which reference should be made without 
further citation in the text. 
cl, a strong nerve to the rhinophore ganglion. Near the base 
of the rhinophore it gives off a slender branch, which forks to the 
integument, and in it forms various anastomoses with other nerves 
in the same region. 
c2 arises just outside of cZ, passes forward and downward over 
the pharyngeal bulb and bifurcates, the inner ramus passing to the 
mouth region, the outer one to the veil. 
c3 arises near c2 and follows a similar course, bifurcating, the 
two branches having the same distribution as those of c2. 
c4, a more slender nerve than c3, arises just external to the 
