60 INTRODUCTION. 



intermissions : when in regular action they contract 

 about sixty times in a minute. One of these hearts 

 has been lately very accurately described by Pro- 

 fessor E. H. Weber, as occurring in a large species of 

 serpent, the Python vivitatus : it is about nine lines in 

 length, and four in breadth; it has an external cellu- 

 lar coat, and a thick muscular one ; four muscular 

 columns run across its cavity, which communicates 

 with three lymphatic vessels, all of which have 

 valves ; the heart has also something like an auri- 

 cular appendage. Dr. Hall's discovery was made 

 near the tail of the eel, and was particularly observed 

 under the microscope. If a young eel, six or seven 

 inches in length, be rolled up in a slip of linen cloth, 

 leaving out a portion only of the tail, it will remain 

 quiet when placed on a long slij:^ of glass, and the 

 pulsation may be readily discovered to be wholly 

 independent of the action or influence of the heart, 

 and the number of beats will be seen to be more 

 than double in the same period of time; they also 

 continue after the heart, properly so called, has 

 been removed. 



There can be no question that such an apparatus 

 as this must greatly promote the important process 

 of absorption; and although it may be supposed to 

 be particularly desiderated in fishes and reptiles. 

 Professor Miiller expresses his conviction, that im- 

 portant discoveries of a similar nature will ere long 

 be made in the hioher classes of animals. 



