418 APPLIED BIOLOGY 



worm-like Balanoglossus, should be viewed for the sake of 

 general acquaintance. Especially note the general appear- 

 ance of Amphioxus, for its stucture is in many points so 

 near the vertebrates that some authors so classify it. Noth- 

 ing about an adult ascidian suggests resemblance to verte- 

 brates, but its larval stage is a tadpole-like animal with 

 some vertebrate characteristics. It degenerates when meta- 

 morphosing into the adult stage. All these simple forms 



FIG. 147. Outline of a vertebrate (rabbit) , showing position of the skeleton. 

 Note that the backbone, which incloses the spinal cord, is in the dorsal 

 part of the body. (From Parker and HaswelL) 



will be interesting to the student who elects advanced courses 

 of zoology in colleges, or who reads the larger textbooks. 



344. General Structure of Vertebrates. The frog, al- 

 ready studied, is a good example of the general plan of body 

 in vertebrate animals. The important points of structure of 

 vertebrates are as follows : (1) dorsal vertebral column ; 

 (2) central nervous system consisting of anterior brain in a 

 skull, and a nerve-cord (spinal-cord) protected by the ver- 

 tebral column; (3) alimentary canal ventral to vertebral 

 column, and heart ventral to alimentary canal; (4) body- 

 cavity containing many organs (name them) ; (5) usually 



