INTERNAL ANATOMY. 309 
Their further relations will be taken up later in connection with the parieto- 
visceral ganglion complex. 
Immediately above the origins of these connectives, on the dorsal surface 
of each ganglion, is found a delicate nerve, pl. 2, arising from two roots. These 
separate roots were only made out in strong sunlight and under a binocular 
dissecting microscope. One of them, the innermost, arises from the pleural 
ganglion itself, the other springs from the cerebro-pleural connective, as shown 
in Plate 2, fig. 1, pl. 2. The second pleural nerves thus formed diverge from 
the pleuro-parietal and pleuro-visceral connectives respectively, with which 
they are at first united in a broad web of connective-tissue, and pass backward 
and upward over the posterior visceral mass, above the spermatotheca and 
enter among the muscles of the dorsal body-wall, immediately in front of the 
pericardium. 
Mazzarelli (1893) denies the existence of any nerves from the pleural (pro- 
to-visceral) ganglia in the Aplysiidae. The writer (1909) has found similar ones 
to those here described in Tethys dactylomela and T. cervina, and they have 
also been noted by Amaudrut (1886) for Dolabella. Further information as to 
the relations and functions of these nerves is very desirable, but the lack of suit- 
able material has prevented it. 
Buccal ganglia.— The buccal ganglia are situated upon the postero-inferior 
surface of the pharyngeal bulb, not upon the superior-posterior surface, as 
stated by Amaudrut (1886). They consist of a pair of rounded ganglia, strongly 
flattened dorso-ventrally, and connected by an extremely short commissure. 
When exposed in ordinary dissection nothing is seen of the ganglia proper, the 
dense connective-tissue capsule which covers them concealing their actual 
shape completely. The outlines of this capsule are indicated by the dotted 
lines on Plate 3, fig. 3. The form of the group so presented is a broad and 
flattened quadrilateral, with no indication of any division into right and left 
halves. The posterior border is slightly concave and is entirely free from the 
bulb, while the anterior one on the contrary is continuous with an overlapping 
fold of its ventral wall. The nerves from the lateral margin are connected 
at their bases by a web-like expansion of the capsule, which is prolonged out 
upon each of them as the nerve-sheath. 
After the complex is removed from the animal, stained in paracarmine 
and cleared in glycerine, the actual flattened oval outline of the ganglia becomes 
visible, and it is seen that they are of much smaller dimensions than those 
shown by the external outline of the capsule, measuring but 1.5 mm. long and 
