314 Dr. E. Rohde on the 



always only upon one side of the segment — to the left in one, 

 to the right in another, but without any definite order — a 

 colossal ganglion-cell, the strong process of which passes to 

 the opposite side, but returns to its original side after a short 

 course, here quitting the nervous system dorsally and running 

 forward applied against the dorsal surface of the ventral cord. 

 The first of these lateral ganglion-cells occurs in the ante- 

 penultimate body-segment. In about fourteen of the following 

 segments anteriorly the number of tlie dorsally-placed colossal 

 nerve-fibres constantly increases by the ganglion-cell pro- 

 cesses which join them in the individual segments, until six 

 or seven of these nerve-fibres run on each side. This number 

 does not increase further, although in each segment a colossal 

 ganglion-cell contributes its process. I have been unable to 

 ascertain with certainty whether in the middle segments of 

 the body on the accession of a new nerve-fibre some of the 

 old ones unite together or come to an end. Sometimes one 

 sees some neighbouring nerve-spaces run together ; but I have 

 not observed any union of the true nerve-fibres situated in 

 them. On the other hand, I several times saw some of the 

 dorsal nerve- fibres quit tlieir places and enter into the ner- 

 vous system, where, after a time, they disappeared. 



Besides the lateral ganglion-cells just described there is on 

 each side, in the middle of each segment, a ventral colossal 

 ganglion-cell the process of which traverses the ventral cord, 

 issuing from it on the other side, and running in the subcuti- 

 cula towards the surface of the body. In these colossal nerve- 

 fibres running peripherally there is no development of a cavity 

 within the sheath. 



By means of transverse sections I have been able to trace 

 out the mode of termination of the colossal fibres in those 

 running from before backwards. In the last segments the 

 sheath becomes gradually thinner, and the nerve-fibres, which 

 are closely embraced by it, more and more distinctly granu- 

 lated. Finally tlie sheath ceases entirely. After a short 

 course the nerve- fibre also disappears without becoming per- 

 ceptibly thinner. In its place in the cross section we see 

 fine ])oints with no definite arrangement. The colossal nerve- 

 fibre has consequently broken up into fine fibrils. 



In Sigalion there are only colossal nerve-fibres running 

 from before backward, and, indeed, in each half of the ventral 

 cord a median one and a ventral one, of which the former is 

 the process of a ganglion-cell situated in the initial portion 

 of the ventral cord ; while the ventral fibre, in accordance 

 with the conditions in Sthenelais, owes its origin to a ganglion- 

 cell occurring; at tlie end of the brain. 



