INTRODUCTION. xliii 



larity and indefmiteness are most apparent and striking*. 

 The so-called nerve-threads exhibit no constancy, either 

 of number or direction ; they do not seem to have any 

 special aim. They reach the wall of the cell or stolon 

 now here, njw there, as if at haphazard. They are 

 found directing themselves to the most unlikely spots, 

 and conducting the (supposed) nervous influence to 

 points where it would seem to be least wanted. Their 

 behaviour certainly is much more that of stray sarcodic 

 filaments than of the servants of a regularly organized 

 and essential system. This indefiniteness in the struc- 

 ture of the plexus had attracted my attention before I 

 had any misgivings as to the correctness of Midler's 

 views ; and it now seems to me to supply one of the 

 strongest arguments against them. 



iii. In essential structure the fuuiculus agrees with 

 the cord, with which it is directly connected at the base 

 of the cell. It is contractile, as already mentioned, and 

 in some measure plays the part of a muscle. Its con- 

 tractility no doubt arises from the modification of some 

 of the fusiform cells composing it, out of which, it would 

 seem, in all cases the muscular tissues are formed. It 

 is a kind of cable, attaching the polypide to its cell, and 

 so organized as to admit of the free movement of the 

 former as it issues from its dwelling and again seeks 

 its shelter. Whether we regard its structure or its uses, 



* The plexus described by Miiller in the branch has its equivalent in the 

 filamentary offshoots from the funiculus in the roceciuiu ; and any student of 

 tin- Pulyrua must have noticed their great irregularity and apparent aim- 

 leosnese. Claparede has remarked, "On ne trouverait jK-ut-ctn> pas deux 

 logos oil le plexus soit semblable a lui-menie." Sniitt has also observed 

 that the plexus varies greatly in tli<> dillon-nt evils of Memb. mtmbranacea, 

 and that the same is the case with the (so-callod nervous filaments in fi 

 pocellaria scrnponti (op. df. p. 3'J). 



