INTERNAL ANATOMY. 339 



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 ganghon, is found a dehcate nerve, pi. 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, pi. 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. 



MazzareUi (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 Tcthys 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 gangUa, 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 conceaUng their actual 

 shape completely. The outhnes 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 di\asion 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-Kke 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 outUne of the ganglia becomes 

 visible, and it is seen that they are of much smaller dimensions than those 

 shown by the external outUne of the capsule, measuring but 1.5 mm. long and 



