In the rays and lampreys, the capillaries being so very much larger, 

 ^-jVs- m diameter on an average, can of course be more readily 

 distinguished, but even these require a good microscope for their 

 due exhibition; which may account in a great measure for the 

 silence, on this point of anatomy, of all the authors whom I have 

 consulted on the subject of the circulation in the respiratory organs 

 of fishes. To fill up a certain portion of this hiatus, and to show 

 how wonderfully minute are these capillaries, and yet in their ar- 

 rangement so characteristic of the vessels performing a similar office 

 in the higher orders of animals, this paper has been brought before 

 the Society on the present occasion. 



