AMPHIOXUS. 



303 



The brain has a single ventricle or cavity and two pairs 

 of cranial nerves. The spinal cord gives off paired spinal 

 nerves. The dorsal nerves are sensory, the ventral are 

 motor, and they do not join. 



P'ig. 216. — Median Section of Brain of Amphioxus. 



(After KuPFFEK.) 



Neural Tube. Ganglion Cells. 



—^ Unpaired 



Olfactory 

 Lobe. 



Infundibulum. 



Pigment Spot. 

 Cerebral Vesicle. 



The front wall of the brain has a simple unpaired mass 

 of pigment, probably a very simple eye. ^Over 

 the brain there is a pit or depression, called 

 the olfactory pit. 



Fig. 217. — Oblique Section of Amphioxus through the 

 Pharyngeal Region. 



Nephridium, 



Coelomic Cavity, 



Glomerulu 



Branchial Blood- 

 vessel. 



Branchial Bar, 



Skeletal Plate, 

 Ventral Blood-vessel. 



Notochord. 



./ Dorsal Blood-vessel 

 (paired). 



Coelomic Canal. 



Branchial Blood- 

 vessel. 

 Branchial Bar. 



Atrium. 



Endostylar Coelom. 



A secondary or tongue-bar is cut through on the left, a primary bar on the 

 right. The section passes along A B in Fig. 213. 



The coelom leads to the exterior by numerous Jiephridia 

 which open into the atrium. They are in the pharyngeal 

 Excretory ^^^i^i^ ^i^d open over each tongae-bar. There 

 is also a large pair of atrio-c^elomic funnels lead- 

 ing from the coelom into the atrium. 



