THK FAMILY OF EKI.S. 323 



fishes are better qualified to discern external objects, or to 

 employ their faculties in their own pursuits; and several 

 instances have been mentioned of the consciousness they have 

 shewn of kind treatment, so as to have become familiar with 

 those who offered them food. Aristotle has noticed that they 

 were attracted with agreeable scents, and Ellis says of some 

 in the South Sea Islands that they came to be fed at the 

 sound of a sharp whistle. 



The remarkable sensibility of touch in the tail of this 

 family of fishes has been already noticed, but we owe to Dr. 

 Marshall Hall the knowledge of a particular organization of 

 the blood-vessels of this part, which beyond doubt is closely 

 connected with the uses to which this organ is sometimes 

 applied. This eminent inquirer remarks, "It has been supposed 

 that the pulmonic heart alone, with the aid of some subsidiary 

 powers of the circulation, propelled the blood. I have dis- 

 covered in one species of fish that which will lead us to 

 view this opinion with distrust, and which will point out to 

 us the fact of an unsuspected addition to the power and 

 action of the heart in some species of animals. This structure 

 is seen, even with the naked eye, in the tail of the Eel. 

 Its form, action, and connexions are, from the degree of 

 transparency of the part, still better traced by the assistance 

 of the microscope. Placed under this instrument, a particular 

 spot near the extremity of the tail of the Eel, easily dis- 

 covered, has the appearance represented" in "the drawing of 

 the ventricle of this caudal heart. The different vessels unite 

 and form a connexion with this ventricle near its highest 

 point." 



The course pursued by the blood in these vessels "uniformly 

 tends towards the highest point of the ventricle; from this 

 point it seems to be slowly propelled or drawn into the ventricle; 

 by a sudden contraction of this it is gathered into a drop, and 

 propelled with great velocity, and at first with the peculiar 

 appearance of successive drops, along a vessel which ascends 

 along the inferior spinal canal, and which must, although it 

 pursues a direction towards the heart, be considered an artery." 

 "The action of this caudal heart is entirely independent of the 

 pulmonic heart; while the latter beats sixty, the former beats 

 one hundred and sixty times in a minute. It continues for a 



