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MR. A. HANCOCK ON THE ANATOMY OF DORIDOPSIS. 201 
can be distinguished ; and thus the mass is seen to be formed of the usual three pairs 
of ganglia—namely, the cerebroid (a a), the branchial (b), and the pedal (c). The two 
former are fused into a transversely elongated mass, which lies across the upper surface 
ofthe proboscis. The pedal form a similar but smaller mass beneath that organ. 
The cerebroid compose the central portion of the upper mass, and lie one on each side 
of the median line, across which they are fused. Their anterior margin projects a little 
beyond that of the branchial ganglia, which are placed on either side, forming two 
rounded lateral lobes. The pedal ganglia are two oval masses, with their outer ex- 
tremities fused to the under surface of the branchial, and their inner extremities united 
to each other across the median line below the proboscis, thus completing the nervous 
collar around the base of that organ. The branchial ganglia are likewise united below 
the proboseis by a slender commissural cord (7), the ends of which are united to the 
lateral portions of the ganglia. At the attachment of the right extremity there is 
a minute rounded ganglion (£), apparently the homologue of the visceral in Doris. This 
eommissure corresponds to the third cord of the sub-cesophageal collar of that form. 
The cerebroid have attached to the upper surface of the anterior margin, next the 
median line, a pair of well-developed, rounded, sessile ganglia, the olfactory (d), each of 
which gives a large nerve (e) to the dorsal tentacles. Three other pairs of nerves (f) 
eome off from the under surface of the anterior border of the same ganglia external to 
the olfactory, and go to supply the anterior part of the oral apparatus. There are no 
optic ganglia or nerves, the eyes (p) being sessile on the upper surface of the cerebroids 
at the external margins of the olfactory ganglia. 
The branchial ganglia give off each from the upper surface towards the lateral margin 
three pairs of large nerves (g), all of which are distributed to the mantle. Two other 
pairs (4) come off at the junction of the branchial with the pedal ganglia, and go, appa- 
tently, to the external envelope at the sides of the body, though these were not satis- 
factorily traced to their destination. From the outer posterior margin of the pedal 
ganglia issue three stout nerves (i), all of which go to supply the foot. 
The buccal ganglia (m and fig. 2e), or the infra-cesophageal, are a pair of small pyriform 
bodies placed close together on the under surface of the oesophagus or crop, immediately 
in front of and between the rudimentary salivary glands, consequently at the posterior 
extremity of the enlarged portion of the proboscis, which we have seen corresponds to 
the buccal organ of Doris. These ganglia are united to each other by a very short com- 
missure, and to the under side of the cerebroids by two exceedingly long commissural 
cords (fig. 57), which pass from the pointed extremities of the ganglia. The great length 
of these cords is necessitated by the action of the proboscis. From the broad or opposite 
extremity of each ganglia a nerve (n) is given off, which is applied to the surface of the 
sophagus Or crop, and has been traced as far as the point where the latter enters the 
liver-mass, This pair of nerves is equivalent to that which we have named in Doris the 
sastro-æsophageal or par vagum. Here, however, it will be observed that there are no 
Sastro-æsophageal ganglia, but that the nerves come off directly from the buccal ganglia. 
„ese nerves and their ganglia, together with the minute visceral ganglion in con- 
nexion with the right branchial, are the ‘only indications of a splanchnic system that 
