EMBRYOLOGY. 145 



6. The liver. 



7. The pancreas. 



8. The lungs. 



9. The heart. 



10. The kidneys, pronephros or mesonephros. 



11. The reproductive organs. 



Push a bristle into the water-pore, and then carefully 

 open the branchial chamber. 



12. Examine the internal gills and arches. 



13. Count the number of arches. 



14. Look for the first pair of feet. 



15. Open the pericardium. 



16. Find: 



(a) The ventricle. 



(6) The auricles. 



(c) The sinus venosus and its branches. 



(d) The aortic bulb, divided into two parts 



and each of these again into three parts. 

 Trace these to the gill-arches. Note 

 that the branch to the third arch divides 

 again. 



Open the mouth and the pharynx by a ventral longi- 

 tudinal cut. See : 



17. The sieve -like arrangement of the gill-arches. 



18. The dorsal aorta, double in the gill region, 



one on each side receiving the vessels from 

 the gills. 



19. Find the posterior feet. 



20. Of what structures is the tail made up ? 



