262 PROFESSOR MARSHALL AND EDWARD J. BLES. 



24. The carotid gland is not a persistent gill, but is formed by 



elaboration of the direct connection between the afferent 

 and efferent vessels of the first branchial arch, which, in 

 place of being a simple passage, becomes plexiform. 



25. The pulmonary and cutaneous arteries develope at an early 



period as diverticula from the dorsal part of the efferent 

 vessel of the fourth branchial arch, shortly before this 

 joins the aorta. 



26. By enlargement of the direct connections between afferent 



and efferent vessels at the bases of the branchial arches 

 at the time of the metamorphosis, an increasing quantity 

 of blood passes from the heart to the aorta without going- 

 through the gills. Increased work is thus thrown on the 

 lungs as respiratory organs, while the gills gradually 

 atrophy. 



27. The first branchial efferent vessel becomes the carotid arch 



of the adult. 



28. The second branchial efferent vessel becomes the systemic 



arch of the adult. 



29. The third branchial efferent vessel loses its connection with 



the aorta, gradually atrophies, and ultimately disappears 

 completely about the end of the first year. 



30. The fourth branchial efferent vessel becomes the pulmo- 



cutaneous arch of the adult : the part of the vessel dorsal 

 to the origins of the pulmonary and cutaueous arteries, 

 which at first opens into the aorta, becomes solid, and 

 then disappears. 



31. The part of the aorta between the carotid and systemic 



arches usually becomes solid, but may remain open even 

 in the adult. 



32. The glomerulus of the head kidney arises as a bulging of 



the ventral surface of the aorta, which soon becomes 

 sacculated. The glomerulus is large so long as the head 

 kidney is active, but then diminishes greatly in size. 



D. General Points. 



33. Throughout the early stages of development there is a 



striking resemblance in arrangement, relations, and pro- 



