MILLER — CONTRIBUTIONS FROM ANATOMICAL LABORATORY. 203 



THE LUNG OF Neciurus macuUtus. 



The lungs of Neclurus consist of two long, narrow, transpar- 

 ent membranous sacs, which extend backwards into the abdomi- 

 nal cavity dorsal to the other viscera. Their outer surface is 

 perfectly smooth and is covered by a layer of the peritoneum 

 lining the pleuro-peritoneal cavity, thus forming a mesentery 

 which attaches them to the dorsal body wall along almost their 

 entire length. In a full-grown specimen, whose lung is from 

 100-125 mm long when distended, less than 25 mm is free. 

 Each lung is a perfectly simple sac, no septa being developed, 

 and their cavities open into the pharynx through a common mem- 

 branous tube running in the dorsal wall of the pericardial cav- 

 ity. This tube represents the trachea of higher vertebrates. 



The epithelium, which forms the outermost layer (serous 

 layer) of the lung of Necturus, varies in size and outline in the 

 various parts of the lung, as may be seen from PI. 3, figs. 1, 2 ; 

 PI. 4, fig. 3. Between the large blood-vessels and especially in 

 the anterior part of the lung, the epithelium is of the common 

 type, as shown in PI. 3, fig. 1. It consists of large, thin, ir- 

 regular cells with comparatively smooth boundaries. The nuclei 

 of these cells do not seem to occupy any one characteristic posi- 

 tion, but are found in all parts of the cell. Toward the pos- 

 terior end and along the sides of the blood-vessels we find the 

 cells taking on a longer and a narrower shape, making them ir- 

 regularly oblong, as shown in PI. 3, fig. 2. The nearer we ap- 

 proach the tips of the lungs, the narrower and longer do the cells 

 become. Between the lateral branches of the blood-vessels we 

 very often find whorls of cells, centering around a rather large 

 irregular one. Covering the blood-vessels and lymphatics we 



