NERVES. 371 



the central chamber is bifid, the nerve tube being also 

 divided ; in others a single corpuscle will be found to contain 

 two distinct chambers and nerve tubes, each being surrounded 

 by a certain number of capsules, but which again are them- 

 selves included in a number of other capsules which embrace 

 both the sets of inner membranes : again, in other instances, 

 two Pacinian corpuscles, entirely formed, but yet not alto- 

 gether separated from each other, being connected by a few 

 of the capsules will be situated upon a single primitive nerve 

 tube : a fourth peculiarity, which may be noticed more fre- 

 quently than any of the others, is the curling back of the 

 extremity of the central chamber, the innermost capsules 

 describing the same curvature. (See Plate XLVLj^s. 4, 5.) 



DEVELOPMENT AND REGENERATION OF NERVOUS TISSUE. 



Development of nerve fibres. The following is the account 

 given by Schwann of the development of the nervous cords 

 as rendered by Willis in his translation of Wagner's Phy- 

 siology, the references to the figures only being omitted. 

 " The nerves appear to be formed after the same manner as 

 the muscles, viz. by the fusion of a number of primary cells 

 arranged in rows into a secondary cell. The primary ner- 

 vous cell, however, has not yet been seen with perfect pre- 

 cision, by reason of the difficulty of distinguishing nervous 

 cells whilst yet in their primary state from the indifferent 

 cells out of which entire organs are evolved. When first a 

 nerve can be distinguished as such, it presents itself as a pale 

 cord with a longitudinal fibrillation, and in this cord a multi- 

 tude of nuclei are apparent. It is easy to detach individual 



filaments from a cord of this kind, in the interior 



of which many nuclei are included, similar to those of the 

 primitive muscular fasciculus, but at a greater distance from 

 one another. The filaments are pale, granulated, and (as 

 appears by their farther development) hollow. At this 

 period, as in muscle, a secondary deposit takes place upon 

 the inner aspect of the cell membrane of the secondary ner- 



