Turner, Nervous System of Cypris. 29 



seem. Dr. Wenzel Vavra confesses that " Die ersten drei Gan- 

 glien stehen sehr gednmgt.'' Although in the adult the sub- 

 oesophageal ganglion of Cypris is an indivisible unit, yet my 

 investigations lead me to believe that it has been compounded 

 out of at least three pairs of distinct ganglia. Now if by say- 

 ing that the first three ganglia are closely compacted Wenzel 

 Vavra means that they are compacted sufficiently to form a tri- 

 une ganglion then our views harmonize. 



From this compound ganglion arise the following five pairs 

 of nerves : nerve of the upper lip, mandibular nerve, nerve of 

 the lower lip, thoracic nerve. 



The two halves of this ganglion are connected by three 

 transverse commissures. 



The first pair of ganglia behind (caudad of) the sub-oesoph- 

 ageal ganglion gives off a pair of nerves to the second maxillae. 



From the last ganglion arise two pairs of leg nerves and 

 one unpaired abdominal nerve. 



In the region of the sub-oesophageal ganglion the ventral 

 chain lies above (dorsad of) the endoskeleton, while back of that 

 region it lies below (ventrad of) the endoskeleton. 



In the region of the sub-oesophageal ganglion the nerve 

 cells are confined to the ventral and lateral surfaces of the gan- 

 glion, while in the rest of the chain, the nerve cells occupy all 

 of the periphery and also the mesal plane. 



Root ganglia. — At the origin of certain nerves there is a 

 mass of ganglion cells. The ganglion is often quite intimately 

 united with the central nerve chain. 



NERVES. 



The principal nerves of Cypris are: the optic, the anten- 

 nulary, the antennary, the labial, the mandibular, the labral, 

 the two maxillary nerves, the thoracic, the two leg nerves and 

 the abdominal nerve. 



Optie Nerve. — The optic nerve arises from the apex of the 

 optic ganglion, which is also the apex of the brain. In Cypris, 

 Cyprinotiis and allied forms examined by me, this is a median 

 unpaired nerve. At a distance from the brain which varies 



