EXPLANATION OF THE PLATES. 



AMPHIOXUS LANCEOLATUS.— Plates I. II. page 371. 



Fig. 1. A lateral view of Amphioxus lanceolatus. As the specimen 

 when sketched was slightly compressed between two plates 

 of glass, it is represented of greater depth than the animal 

 exhibits in its natural condition, a The month, with the 

 oral filaments ; b the abdominal fold of the left side : the 

 fold is semi-transparent, so that the lower surface of the 

 abdomen is seen through it ; c the anus, with one fin before, 

 and another behind it ; d the dorsal fin : the vesicular 

 germs of the rays are seen in all these fins, and the 

 splanchno-ribs are also visible through the abdominal 

 parietes ; e the length of the specimen. 



Fig. 2. The abdominal aspect of the specimen. a The mouth ; 

 b I the abdominal folds ; c the anus ; d the heart. 



Fig. 3. A lateral view of the same specimen after the removal of the 

 integuments, including the abdominal folds and the sofl 

 parts of the fins, a The mouth, with the oral filaments : 

 b the abdominal muscle, with the splanchno-ribs seen 

 through it ; c c the heart ; d the anus ; e the vesicular 

 no* of the rays of the anterior, / those of the posterioi 

 anal fin : these germs do not, like the soft parts, extend to 

 tie- extremity of the tail ; g the germs of the rays of the 

 dorsal tin, -which, like those of the anal I'm, do not extend 

 along the tail ; h h the lateral muscular bundles separated 

 by the needle, so as to display in their intervals the " chorda 

 dorsalis," and tie- dorsal and ventral branches of the oen 

 i the tii-t pair of nerves; k the Becond pair, analogous t>> 

 the trifacial, the dorsal and ventral branches of which 

 extend along the bases of the fins to join the branches of 

 the other nerves. Tins dissected specimen is flattened by 

 lit compre rion, in order to display the various part- with 

 greater distinctn 



I . l. The integuments have been removed from the tail, but the 

 abdominal folds have been left. The abdominal muscle, 

 VOI* i. b 



