949 SCIENTIFIC RESULTS OF THE 
three distinct commissures, which are nearly as long as the diameter 
of the ganglia. From the outer part of the right visceral ganglion 
issues a nerve nearly as long as the transverse diameter of the whole 
central nervous system and swelling to a rather large ganglion (gangl. 
penis) at the root of the penis; this ganglion contains only rather 
small cells and gives off three or four strong and several thinner nerves 
(Plate X, fig. 15). The part of the brain which gives off the nervus 
opticus, simulates a ganglion. The proximal ganglia olfactovia bulbi- 
form, somewhat smaller than the buccal ganglia, but much larger than 
the distal ganglia olfactoria; the buccal ganglia flattened, rounded, con- 
nected by a rather short commissure ; the ganglia gastro-cesophagalia 
rounded, having about one-fifth of the size of the last, containing one 
very large cell and a few smaller. 
The eyes with black pigment and yellowish lens. The otocysts 
lying at the hinder part of the cerebral ganglia, as large as the eyes; 
with numerous small otokonia, which in the specimens from Tiel, 
were not much calcified. No trace of spicula in the leaves or other 
parts of the rhinophoria. ‘The spicula of the skin were, so to speak, 
limited to the margins of the mantle and of the foot; in the last they 
were chiefly arranged perpendicularly or obliquely against the margin, 
except that in the foremost and hinder part of the sole some few spic- 
ula were seen scattered. 
The amount of spicula in the skin seems to vary notably in the 
Acanthodoris pilosa, as seems to be the case in general in different 
forms of Doridide, especially, as far as hitherto known, in the Poly- 
ceratide (Polycera, Ancula). (Cf. Meyer and Moebius, Fauna der 
Kieler Bucht, I, 1865, pp. 52, 60.) Frey and Leuckart (Beitr. zur 
Kenntn. wirbellose Thiere, 1847, p. 145, described a very regular 
position of the spicula, but not, as it seems, in accordance with nature. 
In the margin of the mantle the spicula were arranged as figured by 
Alder and Hanc., 1. ¢., Part VII, Pl. 48, supplem. fig. 1, only more con- 
centrically at the transition from the margin to the side of the body; a 
narrow belt of spicula crossed the back before the region of the gill. 
Some spicula were also seen in the tentacles. The spicula reached a 
notable length (at least 0.6 mm.), in old individuals they were more 
calcified than in younger ones. The skin was filled with unicellular 
olands, especially in the dorsal papill.! 
The mouth-tube was wide and strong, about 1.5 mm. long; the 
bulbus pharyngeus in the largest individuals about 2.75 mm. long, by 
1 Cf. the (not very good) fig. 6 by Meyer and Moebius. 
