54 ANIMAL BIOLOGY. [Part I. 



6. In all three the position of the heart is the same, just 

 above the sternum. 



7. Notwithstanding pronounced differences, chiefly due to sup- 

 pression, the arrangement of the great vessels which enter and 

 leave the heart is fundamentally the same. 



8. Although they differ considerably in form and structure, 

 and also to some extent in position, the relations of the lungs to 

 the trachea, and of the trachea to the oesophagus are essentially 

 the same. 



9. In all. the alimentary canal is suspended in the body-cavity 

 or coelom, like a smaller tube within a greater ; but in the head 

 and neck the greater tube is wanting. 



19. In all the liver and pancreas have similar positions and 

 relations. 



11. In all the kidneys are similarly placed, and the ureters 

 pass backward to open near the termination of the alimentary 

 canal. 



12. Although the testes of the rabbit have undergone a 

 remarkable change of position, these organs are in all three types 

 essentially similar structures ; but the connection of the testes 

 of the frog with the kidneys, and the possession by that animal 

 of a common urino-genital duct constitutes an important ana- 

 tomical difference. 



13. Notwithstanding the suppression of the right ovary and 

 oviduct in the pigeon, the position and relations of these parts 

 in our three types are fundamentally similar. 



14. Many of these fundamental resemblances hold good for 

 the cod also. The student should note for himself how far they 

 extend. 



