NERVES. 369 



cerned with the naked eye^ and the entire of their structure 

 followed out without even the employment of a reagent : it 

 is therefore in these animals that they are studied to most 

 advantage. 



The Pacinian bodies vary greatly in size, but are usually 

 as large as the head of a pin of ordinary magnitude ; they 

 are of an oval or pyriform shape, are perfectly translucent, 

 attached to the nerve filaments by short pedicels, and occur 

 either singly or sometimes in pairs. (See Plate XL VI. 

 fig. 1. 



So large are these peculiar bodies that the whole of their 

 structure may be followed out with object glasses of an inch 

 and half- inch foci; when examined with these magnifying 

 powers each Pacinian body is observed to consist of nu- 

 merous concentric lamellae or capsules disposed with much 

 regularity ; these lamella are formed of white fibrous tissue, 

 contain numerous nuclei in their substance, and are separated 

 from each other by distinct intervals which contain fluid; 

 the spaces intervening between the plates do not commu- 

 nicate and diminish gradually but regularly from without in- 

 wards, so that the central lamellae are almost in contact with 

 each other, from which cause they present a darker aspect 

 than do those having appreciable spaces dividing them the one 

 from the other : these capsules have been distinguished from 

 the rest by the term the " inner system of capsules." It is 

 this regular disposition of the lamella? together with their 

 gradual approximation which imparts so beautiful an ap- 

 pearance to these strangely constituted organs. The cap- 

 sules, however, are not continued to the very centre of the 

 Pacinian body ; but in that situation a cavity, having a 

 somewhat elliptical form and filled with fluid exists. This 

 cavity opens externally by means of a canal which pierces the 

 whole of the lamellae and the sides of which canal are formed 

 by the union of those lamellae : into this canal a single nerve 

 tube passes, enters the central cavity just described, which it 

 traverses from end to end in a straight line, terminating in a 

 slightly enlarged extremity, which is described as being at- 

 tached to the inner wall of the distal end of the central cham- 



oo4 



