206 BULLETIN OF THE UNIVERSITY OF WISCONSIN. 



epithelial cells were found over both the artery and vein, down 

 to the apex of the lung, while a few were also found between 

 them. This is not the case in the newt according to Stirling , 

 'the ciliated epithelium being found only ov^r the pulmonary 

 vein and its principal branches, while a plexus of capillaries lies 

 over the artery. Williams, in contradistinction to Stirling, fig- 

 ures the ciliated epithelium over both the artery and vein of the 

 newt. In Necturus I found a plexus of capillaries, as well as 

 the ciliated epithelium over both artery and vein. 



THE ELASTIC EIBERS. 



The elastic fibers of the lung of Necturus form an exceedingly 

 complex network, as shown in PL 6, fig. 9. The fibers are of 

 two types, the coarser ones being nearer the surface, and form- 

 ing wider meshes than the finer and deeper ones. They also run 

 more generally in a direction parallel to the long axis of the 

 lung. The meshes of the fine fibers are exceedingly intricate, 

 especially around the blood-vessels. 'Stirling describes the elas- 

 tic fibers as forming a layer lying between the endothelimn and 

 the layer of smooth muscle, but this cannot be said of the lung 

 of Necturus. Fibers are found scattered throughout the 

 walls of the lungs. PI. 7, figs. 11, 12, show longitudinal and 

 cross sections of the lung of Necturus taken near blood-vessels 

 which show the fibers as dots or lines, according as they are cut 

 transversely or more or less longitudinally. 



THE MUSCLE FIBERS. 



The muscle fibers are of the involuntary type and run prin- 

 cipally in a circular direction, thus forming a tubular founda- 

 tion for the lung. The nuclei of the fibers are shown in PL 7, 

 figs. 11, 12 ; PL 8, figs. 13, 14. At the tip of the lung the fibers 

 form an intricate network, running in all directions. 



Stirling mentions a difference in position of the vein and 

 artery with reference to the layer of muscle fibers, the artery 

 lying internal to this layer, while the vein lies externally to it. 



