EXPLANATION OF PLATE I. 



Fig. 1 . A branchial lamina of a common eel, showing the concave edge along which 

 the branchial vein runs, and ihe small transverse plica; or folds of the 

 mucous membrane. 



Fig. 1 a. A portion of the same more highly magnified, to show the capillary plexus 

 upon the fold of the mucous membrane. 



Fig. 2. One of the laminae of the common eel, showing the folds of mucous mem- 

 brane given off from both sides of the lamina. 



Fig. 2 a. A portion of the same magnified one hundred diameters. 



Fig. 3. One of the laminae of a common eel, showing the convex border on which 

 the branchial artery, and the concave one on which the branchial vein 

 runs, and the folds of mucous membrane between them. 



Fig. 3 a. A portion of the same magnified one hundred diameters. 



Fig. 4. A portion of one of the laminae of a lamprey (JPelromyzon marinus), showing 

 the broad transverse folds of the mucous membrane. 



Fig. 4 a. A portion of the same magnified fifty diameters, to show the capillary plexus 

 on the folds. 



Fig. 5. A portion of one of the laminae of a ray (Raia balis), showing the folds of 

 the mucous membrane. 



Fig. 5 a. A portion of the same magnified fifty diameters ; it shows the large size of 

 the capillaries composing the plexus. 



