NERVOUS SYSTEM OF CRUSTACEA 439 



From the same level from both sides, especially from median 

 cells, d) Probably fibers to and from lateral branches of gan- 

 glia, although this was not clearly demonstrated (fig. 4) . 



SOME GENERAL CONCLUSIONS 



The study of these nervous systems shows certain advantages 

 due to the nature of the material and the method. There is 

 less distortion because with whole mounts no heat was used. 

 There is also a more perfect picture presented than in most 

 methylen blue preparations because all the cells show. When 

 large ganglion cells were at the edge of the preparation quite 

 a little could be seen of their finer structure and the fibers 

 and fibrils were often presented with great clearness. I 

 believe that, although the grosser processes are important, 

 that the fibrillar connections are more important in determin- 

 ing the intimate relationships o£ cells to each other. It seems 

 probable from these observations that any cell may have its 

 cytoplasm penetrated by fibrils which are directly connected 

 with other cells, while its one or two main branches carry out 

 fibrils in larger masses, break up into fibrils and by usual methods 

 are not followed farther. 



The variation in the number of cells in similar segments 

 suggests the probability that the nervous system acts not so 

 much through individual innervation of special areas by special 

 cells, as by a more general innervation by groups of cells. In 

 the course of evolution in more specialized forms it may be that 

 individual functions may more nearly be connected with indi- 

 vidual cells or small groups. 



