AMPHIOXUS 19 



Specialised Characters. 

 Atrium ; 



Extra large number of gill-slits, having lost corre- 

 spondence with the segmentation of the body ; 

 Tongue-bars ; 



Asymmetry of oral hood and early development ; 

 Extreme anterior extension of the notochord. 



The large number of its primitive characters show that 

 Amphioxus is a primitive animal, i.e. related to the original 

 ancestors from which all chordates evolved. The secondary 

 characters which Amphioxus possesses, however, show that 

 it is not on the direct line of chordate descent. 



Literature 



Bourne, G. C. An Introduction to the Study of the Comparative Anatomy 

 of Animals. Vol. 2. Bell, London, 191 5. 



Delage, Y., et Herouard, E. Zoologie Concrete. Vol. 7. Les 

 Procord£s. Schleicher Freres, Paris, 1898. 



Goodrich, E. S. On the Structure of the Excretory Organs of Amphioxus. 

 Quarterly Journal of Microscopical Science. Vol. 45, 1902 ; and 

 Vol. 54, 1910. 



Orton, J. H. The Ciliary Mechanisms on the Gill and the Mode of 

 Feeding in Amphioxus. Journal of the Marine Biological Association. 

 Vol. 10, 1913. 



Willey, A. Amphioxus and the Ancestry of the Vertebrates. Columbia 

 University Press, 1894. 



