THE CLASSIFICATION" OF THE OPHIDIA. 191 



smaller lung lies to the right side and ventrally, while the larger one lies to the left 

 side and dorsally. In some species the dorsal and ventral relation is more pronounced 

 than in others. In the Colubroidea the right or ventral lung is generally present, but 

 of very much reduced proportions, the usual size being from two to five millimetres in 

 length. It is connected with the other lung by a foramen which perforates the trach- 

 eal cartilage at a point a little beyond the apex of the heart and opposite to the prox- 

 imal part of the dorsal lung. It is sometimes connected to the dorsal lung by a 

 short tube, in which cartilaginous half rings are seen in but two of the genera ex- 

 amined, viz., Heterodon and Conophis. The lumen of the rudimental lung may be 

 lined by the same reticulate structure as is seen in the dorsal lung, or its walls may 

 be smooth. In some Colubroidea the rudimental lung is absent, but such species are 

 relatively few. 



The dorsal lung may present proximally alongside of the trachea an auricle or 

 pocket, and this is so developed in the genus Heterodon as to reach to the head with- 

 out communication with the trachea other than that furnished by the normal portion 

 of the lung. In the Solenoglypha, without exception, this extension of the dorsal 

 lung is present, and extends to the head, and its lumen is continuous with the trachea 

 throughout its length. The same structure exists in the genera Hydrus and Hydro- 

 phis, and also in the West Indian peropodous genus Ungualia, which differs besides 

 from other Peropoda in having but one posttracheal lung. Finally the tracheal 

 lung, as I have called it, is distinct from the true lung in the water snakes Platurus 

 and in Chersydrus. In the former of these genera the trachea is not separate from 

 the lumen, while in Chersydrus it is distinct. It, however, communicates with 

 the cells of which the lung consists in this genus by a series of regularly placed for- 

 amina on each side. There is no lumen in the tracheal lung of Chersydrus. In the 

 blind burrowing Typhlops we have a still further modification of the tracheal lung*. 

 It is without lumen, and -is composed of coarse cells of different sizes. These have no 

 communication with the trachea or lung that I can discover. It has occurred to me 

 that this structure, which extends from the heart to the throat, may not be a pul- 

 monary organ. 



I have referred to the dorsal and ventral positions of the two lungs. The rudi- 

 mental lung is to the right of the dorsal lung in the Colubroidea, hut in the Ilysiida; 

 it is to the left. It is quite questionable which lung this rudiment in this family 

 really represents. In the Typhlopidse the single lung is on the right side and extends 

 from the heart to the liver. It has the position of the rudimental lung of the Colu- 

 broidea and may represent it. I cannot decide this question without further material. 

 In Glauconia there is but one true lung, and this is ventral in position and originates 



A. p. s. — VOL. XVIII. Y. 



