4 Vertebrata. 



conveys the blood from the alimentary canal to the 

 liver is called the vena portce. 



3. Primary divisions of vertebrates (headless 

 form). There are two primary divisions of vertebrate 

 animals ; the first of these includes only one form, and 

 that the smallest and simplest in the sub-kingdom, 

 remarkable principally for its extremely simple organ- 

 isation. This little creature is named the lancelet, or 

 technically the Amphioxus lanceolatus, and is so called 

 on account of its lancet-like shape, and from its being 

 pointed at both ends. It is a small, flattened, fish-like 

 animal, about an inch and a half long, about a quarter 

 of an inch in depth and an eighth in thickness, found 

 in sandbanks in our own seas. It has been taken 

 in abundance off the coasts of North Carolina and 

 Florida, off the S.W. coast of Ireland, in the Mediter- 

 ranean, and in the Indian and Pacific Oceans. 



This animal has no head, and the notochord 

 stretches from the front to the hinder point ; the 

 neural canal and its enclosed spinal marrow likewise 

 extend for the whole length. The mouth is a longi- 

 tudinal slit, bordered with stiff, bristle-like filaments ; 



' >' T=-T5- 



Diagram of Amphioxus. 



a, mouth; 6, f, g, respiratory region ; c, body cavity ; d, liver ; e, heart; 

 /&-/, digestive canal ; /, notochord ; **, spinal marrow. 



and the pharynx has many lateral slits in its wall, 



