190 AMPHIOXUS. 



I. The Excretory System, 



Three kinds of excretory organs have been described in 

 Amphioxus. 



1. The pigmented canals discovered by Lankester are pos- 



sibly 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 coelomic 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. Miiller's renal papillae are numerous pigmented papillae 



on the floor of the atrial cavity. 



3. Weiss and Boveri have recently discovered a series of 



curved excretory tubules lying in the dorsal coelomic 

 canal along each side of the pharynx. Each tubule 

 communicates with the coelom by one or more open- 

 ings and with the atrial cavity by a single opening 

 on the outer side of a secondary pharyngeal bar, close 

 to its dorsal end. 



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 he 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 he isolated by placing them in 20 per cent, rdbric 



