1 68 



MILLER, 



[Vol. VIII. 



and when a group of the sacs open into a common cavity 

 with no distinct walls, I term it the atrium. From the stand- 

 points of evolution and of development this may not be quite 

 correct, for what is originally an air-sac in a simple lung is 

 converted only in part into the air-sac of the complex lung ; 

 if the terminology is reversed, about the same holds true. 



The Air Passages. 



Amphibian king. — Of the amphibians I have chosen for 

 description the lungs of Necturus maculosus, the common mud 

 puppy of the Mississippi Valley and the great lakes of the 

 the West, and those of the common frog (R. catesbiana). In 



Lung of Necturus. 



Lung of frog. 



Necturus the lungs consist of two elongated cylindrical-shaped 

 bodies, the outer and inner surfaces of which are perfectly 

 smooth (Fig. i). Along the mesial side of the lung is seen 

 the vein and on the opposite side the artery. Lateral branches 

 are given off from each, which give rise to the capillaries. 

 The distribution of the vessels is such, that we find an arterial 

 twig placed nearly equidistant between two venous twigs. 



In the frog (Fig. 2) the lungs are ellipsoid in shape and 

 bluntly pointed behind. The exterior is smooth, but the inner 

 surface is crossed by large bands which extend some depth 

 into the central cavity. These form a coarse network, within 



