170 



Chapter X. 

 THE LANCELET. Amphioxits lanceolatus. 



Amphioxus is a small semi-transparent fish-like animal, about, 

 a couple of inches in length, found in shallow parts of the- 

 Mediterranean and other seas. It is of sluggish habits, and. 

 usually remains buried in the sand, either completely or with 

 the anterior end alone protruding ; but if disturbed it swims 

 actively by rapid lateral movements of the body. 



Though distinctly belonging to the great group of verte- 

 brate animals, Amphioxus is in several important respects 

 simpler and more primitive than any of the more familiar 

 members of the group. Indeed, in spite of its fisn-like appear- 

 ance and habits, the differences between Amphioxus and an 

 ordinary fish, such as a dog-fish or whiting, are of greater 

 morphological importance than those separating fish from the 

 most highly organised vertebrates, such as birds or mammals. 

 It is therefore necessary to divide vertebrates into two main 

 divisions, the first of which, Acrania, includes Amphioxus and 

 a degenerate group, the ascidians ; while the second division, 

 Craniota, includes all remaining vertebrates, from fish tO' 

 mammals. 



I. EXTEENAL CHAEACTERS. 



Take cm adult specimen preserved in spirit, place it in a 

 small dish in weak spirit or water, and examine with a pocket' 

 lens or dissecting microscope. 



a. The shape. Amphioxus is elongated, pointed at- 

 both ends, and compressed from side to side,. 



