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Chapter X. 

 THE LANCELET. Amphioxus 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 fish-Uke 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. 



Owing to its small size it is not practicable to determine 

 all the points of its anatomy by dissection. The external 

 characters should be determined by examination of adult 

 specimens preserved in spirit. The general anatomy is best 

 seen in young specimens, not more than half an inch in 

 length, mounted whole as microscopical prepa/rations ; while 

 the details of structure should be confirmed by microscopical 

 examination of transverse sections through various regions of 

 the body. 



