198 AMPHIOXUS. . 



I The Excretory System. 



Three kinds of excretory organs have been described in 

 Amphioxus. 



1. The pigmented canals discovered by Lankester are 



possibly excretory. These are a pair of short wide 

 funnels, with deeply pigmented walls, placed in the 

 twenty-seventh segment of the body, opposite the 

 hinder end of the pharynx. They lie, one at each 

 side of the body, in the dorsal ccelomic canals above 

 the suspensory folds of the pharynx. Each tube is 

 attached along its outer side to the body-wall, and 

 opens by its wider end into the atrial cavity ; in 

 front it is considerably contracted, but appears to 

 open into the ccelomic canal. 



2. Muller's renal papillae are numerous pigmented papillae 



on the floor of the atrial cavity. 



3. Weiss and Boveri have discovered a series of curved 



excretory tubules lying in the dorsal ccelomic 

 canal along each side of the pharynx. Each tubule 

 communicates with the atrial cavity by a single 

 opening on the outer side of a secondary pharyngeal 

 bar, close to its dorsal end, and contains remarkable 

 hollow cells within each of which is a nagellum. 



K. The Nervous System. 



The nervous system of Amphioxus consists of : (1) the 

 central portion, which, as in other vertebrates, is a tube of 

 nervous matter lying in a sheath of connective tissue imme- 

 diately above the notochord, and extending almost the entire 

 length of the body ; (2) the peripheral portion, which consists 

 of the nerves connecting the central portion with the various 

 parts of the body. 



The nervous system can be well seen in transverse sections 

 of adults, or by examination of young specimens mounted 

 whole. If fresh specimens can be obtained, the entire nervous 

 system can be isolated by placing them in 20 per cent, nitric 



