GANGLION CELLS OF THE CRAYFISH 199 



ganglion is larger than the other two and contains a greater num- 

 ber of ganglion cells, whose arrangement was different from that 

 in the other ganglia. No attempt was made to determine any 

 particular arrangement of the cells in this ganglion. On this 

 ganglion the general effects of the operation were observed as 

 well as the degeneration and disappearance of its cells without 

 respect to their particular position. 



In all these ganglia, each large ganglion cell has a single nerve 

 fiber proceeding from it, which may be traced in favorable sec- 

 tions far enough to determine its course some distance through 

 the ganglion. Retzius ('90) has shown that the fibers from some of 

 these cells pass into the connectives and from others into the lateral 

 nerves. These fibers are non-medullated, having only the sheath 

 of Schwann. The fibers also show very characteristic nerve fibril- 

 lse. These fibrillse are best seen in the large fibers when special 

 methods of fixation are employed. They may also be seen very 

 distinctly in the axis-cylinder within the ganglion cells, where 

 they extend partly around the cell nucleus, though separated from 

 it by a certain amount of the protoplasm of the cell. It is evident 

 from what has been said that these large ganglion cells with their 

 fibers extending outward in the manner described, afford relatively 

 simple conditions for experiments, in which the effects on the gan- 

 glion cells following the cutting of their fibers could be readily 

 observed. 



It was not known how well the animals could endure the in- 

 juries incident to the necessary operations, such as the effects due 

 to shock and the interference with the ventral blood sinus. 

 Throughout the series of experiments, however, little difficulty was 

 experienced from either of these sources. There was but little 

 loss of blood, shock effects soon passed away, and the wounds 

 healed with greater promptness than was anticipated. Aside 

 from the loss of movement of the fifth abdominal segment and 

 those posterior to it, the animals operated upon differed from nor- 

 mal individuals only in that they were slightly less active. 



In operating, an incision was made with a sharp lance through 

 the integument well toward the right side of the ventral surface 

 of the abdomen between the fourth and fifth stern ites. By insert- 



