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Chapter XI. 



THE LANCELET. Amphioxus hnceolatus. 



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

 a couple of inches in length, found in the English Channel, 

 the Mediterranean and other seas. It is by day of sluggish 

 habits, and usually remains buried in the sand, either com- 

 pletely or with the anterior end alone protruding ; but at 

 night, or 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 than any of the more familiar members of the group. 

 Indeed, in spite of its fish-like appearance 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 probably 

 degenerate group, the Ascidians ; while the second division, 

 Craniota, includes all remaining vertebrates, from fish to 

 mammals. 



Owing to the small size of Amphioxus, it is not practicable 

 to determine all the points in its anatomy by dissection. The 

 method of procedure adopted in the case of the other animals 

 dealt with in this book will in consequence be departed from 

 to some extent ; and the present chapter will be arranged 

 under three heads. 



I. A description of the anatomy of Amphioxus. 



