10 ANATOMY OF AM PHI OX US. 



and rotation by the action of the cilia with which the 

 epithelium of the alimentary canal is richly provided. 

 After the digestible elements in the food have been dis- 

 solved in the secretions of the intestinal wall the cord of 

 slime with the attached faeces is duly ejected. 2 * 



The extreme shyness to a bright or sudden light which, 

 as Costa observed, is manifested by Amphioxus, is prob- 

 ably correlated with the presence of black pigment spots 

 in the nerve-cord. If a lighted candle is carried into a 

 dark room in which Amphioxus are being kept in glass 

 jars, the excitement produced among the small fish is 

 indescribable. 



Occasionally it emerges from its favourite position in 

 the sand, and after swimming about for some time it will 

 sink to the bottom, and there recline for a longer or 

 shorter period upon its side on the surface of the sand. 

 When resting on the sand, it is unable to maintain its 

 equilibrium in the same position as an ordinary fish would 

 do, but invariably topples over on its side, indifferently on 

 the right or left side. 3 In the higher fishes, including the 

 lampreys, there is a special apparatus for controlling the 

 equilibrium ; namely, the semicircular canals of the ear. 

 There is nothing of the kind in Amphioxus, but in the 

 Ascidian larva and in the Appendicularias there is, as 

 we shall see, a structure situated in the floor of the brain 

 known as the otolitli, which possibly exercises an equilib- 

 rating influence. 



From what has been said above it follows that Amphi- 

 oxus is an entirely passive feeder ; it does nothing in the 

 way of biting, or even sucking, and has not to search far 

 for its food, but merely takes what is brought in with the 



* This number and others which are scattered through the text refer to the 

 Notes at the ends of the chapters. 



