70 



INTRODUCTION. 



a The termination of a large lymphatic, which begins at 

 the tail and runs upwards on the side of the fish, receiving 

 its branches from the skin and muscles of the trunk at 

 nearly right angles. 



b The upper end of a mucous dwct, which runs upon the 

 side of the fish nearly parallel with the lymphatic a, and 

 which has numerous short branches, with open mouths, 

 which pour out mucus upon the .surface of the skin. 



c is the continuation of the duct b cut open. 



d Another mucous duct, having no communication with 

 b or c, and which discharges its mucus upon the surface of 

 the skin of the under jaw by a number of short branches. 



One of the most remarkable contrivances in 

 the economy of fishes, is their respiration. The 

 medium which contains the air, being fatal to 

 all terrestrial animals which would attempt to 

 inhale them in conjunction, a different apparatus 

 for their employment was necessary, which we 

 find in the form of branchicE or gills, as they 

 are termed, placed near the forward extremity 



