Turner, Nervous Sj'ston of Cypvis. 27 



glion. Although small, yet this supra-oesophageal ganglion is 

 probably compounded out of seven distinct ganglia. These 

 problematic ganglia are : three ganglia that have fused to form 

 the unpaired optic ganglion, two antennulary ganglia, and two 

 antennary ganglia. 



The optic ganglion is located in the roof (dorso-cephalic 

 portion) of the supra-oesophageal ganglion. Although in the 

 adult it is a median unpaired structure, yet its histology seems 

 to indicate that it is a triune structure. The optic nerve arises 

 from the apex of this ganglion. In Cypris and the allied forms 

 examined by me, the optic nerve is a single unpaired nerve; but 

 in NotodroDias, a{;cording to Wenzel Vavra, three optic nerves 

 arise from the brain/ The fact that in Notodromas three nerves 

 arise from the optic ganglion lends support to the view that this 

 is a triune ganglion. However, we must look to embryology 

 for a final settlement of this question, and the necessary data 

 are not at hand. Wenzel Vavra has called this portion of the 

 supraoesophageal ganglion from which the optic nerve arises the 

 fore-brain. 



The paired antennulary ganglia occupy the lateral portion 

 of the supra-oesophageal ganglion [fig. 10]. Wenzel Vavra 

 has called this portion of this ganglion the mid-brain. From 

 the dorsal portion of each side of this ganglion, arises a nerve. 



Further ventrad, but nearer the meson, in the lateral por- 

 tion of the supra-oesophageal ganglion lie the paired antennary 

 ganglia [fig. 10]. A portion of this ganglion lies in the phar- 

 yngeal collar. Wenzel Vavra has called this portion of the gan- 

 glion the hind brain. 



The supra-oesophageal ganglion is connected, by means of 

 a pair of circum-oesophageal commissures, with a sub-oesopha- 

 geal ganglion [fig. 16, 42]. These commissures pass obliquely 

 backwards and downwards (ventro-caudad) from the lateral por- 

 tion of the supra-oesophageal ganglion to the corresponding 

 portions of the sub-oesophageal ganglion. These two commis- 

 sures constitute the pharyngeal collar. This collar is not merely 

 a commissure but it is also the locus of a nerve centre. All along 



