APLYSTA. 233 



the skin on the side of the body anterior to the rhinophore. 

 On the right side it sends a branch to the penis. 



6. The "auditory" nerve (and. n.). This slender nerve 

 arises from the posterior side of the cerebral ganglion, and 

 passes backwards between the cerebro-pleural and cerebro- 

 pedal connectives to the statocyst, which lies in a shallow pit 

 excavated on the surface of the pedal ganglion. 



B. Pleural Ganglia and Nerves. 



The pleural ganglia (pi. g.) are situated laterally to the 

 cerebral ganglia with which they are connected by the short 

 and stout cerebro-pleural connectives. Pleuro-pedal connec- 

 tives are also present, but there are no pleural commissures. 

 From the pleural ganglia arise the long pleuro-visceral con- 

 nectives. That on the right side passes straight to the parietal 

 (supra-intestinal) ganglion lateral to the right salivary gland. 

 The left connective dives ventral to both salivary gland and 

 oesophagus, emerging into view again at the posterior end of 

 the crop, where it swells to form the visceral ganglion, lying 

 adjacent but slightly postero- ventral to the parietal ganglion. 

 Both connectives run dorsal to the aorta. The amount of 

 contraction of the animal may cause some variation in the 

 relative positions of the parts in this region. From the pleural 

 ganglion arises a slender nerve to the body wall. In some 

 specimens there are two nerves on the left side and one on the 

 right (teg. n. 3 and teg. n. 4). The nerve emerges from the 

 anterior portion of the ganglion and passes straight outwards. 

 It has an anastomosis with the posterior tentacular nerve (A3) 

 and with the tegumentary nerve (C5). Although nerves arise 

 from the pleural ganglia in Streptoneura (e.g., Patella), their 

 presence is rare in the Euthyneura, where the infra-intestinal 

 ganglion takes on the work of supplying the reduced mantle. 

 The fact that the visceral ganglion supplies both viscera and 

 mantle region is evidence that this ganglion represents infra- 



