142 HUGH WATSON. 



longer the cerebro-liuccal connectives, the more freely can 

 the odontophore be protruded ; for it is evident that when the 

 buccal ganglia normally lie behind the cerebral ganglia, the 

 odontophore bearing the buccal ganglia can be brought for- 

 ward a distance equal to twice the length of the connectives 

 without moving the cerebral ganglia at all. 



The buccal ganglia are rounded or oval, and joined to 

 each other by a short buccal commissure. As might have 

 been expected, they are proportionately larger and closer 

 together in those forms in which the odontophore is very 

 large than in such species as A. burnupi, in which the 

 odontophore is much smaller. In A. gibbonsi the ganglia, 

 when freed from the connective tissue which surrounds 

 them, are seen to be almost as near to each other as are the 

 cerebral ganglia (PI. XV, fig. 70). 



The Nerves of the Buccal G-anglia. — Three slender 

 nerves arise from the anterior part of each buccal ganglion 

 (figs. 70-72). One of these becomes attached to the salivary 

 duct of the same side, and passes backwards to the salivary 

 glands. The other two go to the oesophagus, one bifurcating 

 soon after it leaves the ganglion. Two more pairs of 

 nerves arise laterally from the ganglia and innervate the 

 sides of the buccal mass and odontophore, one pair going 

 forwards and the other backwards. These nerves are 

 especially large in Apera gibbonsi, in which the parts they 

 innervate are so greatly developed. The anterior lateral 

 nerve passes forwards to the side of the buccal mass in front 

 of the oesophagus, and in this species it is generally united at 

 its origin for a very short distance with the cerebro-buccal 

 connective on the same side. In A. sexangula, on the 

 other hand, this nerve appears to be united near the ganglion 

 with the posterior lateral nerve, a fact which is probably 

 connected with the anterior position of the buccal ganglia in 

 this species. The posterior lateral nerve on each side passes 

 to the sheath of the odontophore, and bifurcates as it does so. 

 The outer and more slender branch, after passing through 

 the external longitudinal muscles, runs down the sides of the 



