SHARP-NOSED EEL. 297 



and mammalia, may be expected ; my researches, as regards 

 these, have however been hitherto unsuccessful." In an- 

 other part of his paper, Dr. Muller observes, " I have never 

 discovered a trace of motion in the cy sterna chyli and ductus 

 thoracicus of mammalia." 



In a conversation with Mr. Owen on this subject, he sug- 

 gested, that as the valves of the lymphatic vessels are very few 

 and imperfect in reptiles and fishes, especially in the latter, 

 these pulsating sacs would seem to be superadded as a com- 

 pensating power in the absence of that mechanism which 

 impresses a definite direction and an unintermitting flow 

 upon the currents of the lymph in the higher vertebrata, 

 especially mammalia. 



I am indebted to the kindness of Dr. Marshall Hall for 

 permission to copy the excellent illustration of this structure 

 in the tail of the Eel, from his very interesting critical and 

 experimental essay on the circulation of the blood. 



In the vignette the arrow-heads indicate the direction of 

 the currents. 





VOL. II. 



