ioo Instinct and Intelligence 



The term cerebrum is applied to the largest 

 section of the brain; it consists of the two 

 halves into which the fore-brain is divided, 

 known as the cerebral hemispheres, united to 

 one another by connecting nerve fibres. 



In the Amphioxus, a small fish-like being, we 

 have an example of a living primitive verte- 

 brate. These animals inhabit shallow seas in 

 almost all parts of the world; although fish- 

 like in appearance, they have neither the struc- 

 ture nor habits of a true fish. 1 An elastic carti- 

 laginous rod (the notochord) extends throughout 

 the length of the body of an Amphioxus, giving 

 support to its muscular and other structures. 

 The animal's central nervous system is formed 

 of a thick-walled tube, nearly co-extensive with 

 the notochord. The bulk of the cord is made 

 up of longitudinal nerve fibres; it contains a 

 central canal, round which are nerve-ganglion 

 cells, some of them of considerable size. At 

 the anterior end of the cord the central canal 

 widens to form a space known as the cerebral 

 vesicle. The nervous matter constituting the 



1 The Introduction to the Study of the Comparative Anatomy 

 of Animals, by Prof. Gilbert C. Bourne, Vol. II., pp. 173, 188. 



