CHOEDATA 



341 



In all the vertebrates there are certain structures called 

 ductless glands. These are always well supplied with blood 

 vessels. They seem to manufacture and to pour into the blood 



Fig. 168. 



Pig. 169. 



pre. c 



Fig 168. Diagram of the heart and branchial arches in Protopterus (one of the Dipno). 

 Position and lettering as in the preceding. ' pre.c, precaval vein, made up of right and left jugulairs 

 subclavians, etc. ; post.c, postcaval, made up of the cardinals, right and left. 



Questions on the figure. — What are the chief differences between the con- 

 ditions here and in the preceding figures: (i) as to the heart: (2) as to arteries; (3) 

 as to veins; (4) as to lungs? 



Fig. 169. 



Diagram of the heart and branchial arches in the Frog. 

 Z., lungs; l.a., left auricle; r.a., right auricle. 



e.g., carotid gland; 



Questions on the figure. — How does the heart differ from that of the Dipnoi? 

 How many branchial arches of the aorta are shown? What evidences can you 

 find by comparison that the pulmonary arch is derived from the 3d or 4th branchial ? 

 What evidences that the carotid and systemic are the first and second respectively? 

 Compare with the table on page 344. Is there anything to indicate that the im- 

 purest blood in the heart will go to the lungs? 



directly certain secretions that have effect on even remote parts 

 of the body. These glands may properly be discussed as a 

 part of the circulation since they have no other outlets. These 



