INTRODUCTION TO THE METAZOA 



67 



carries impulses outward from the cell body and this process 

 is called a neurite or an axon. 



In most of the higher Metazoa, the nerve 

 cells are grouped into masses which are called 

 ganglia. The neurites and dendrites form 

 part of the fibrous portion within the ganglia 

 and continue in groups out from the ganglia 

 as important constituents of the nerves of the 

 peripheral nervous system. 



By very special histological technic the 

 cytoplasm of a neruon and its processes is 

 shown to contain various fibrillar structures 

 (Fig. 44). It is thought that nerve impulses 

 are transmitted along these fibers rather than fibriilae in ganglion 

 through the general cytoplasm. In addition, cell of a leech. {After 

 much of the cytoplasm of nerve cells contains 

 deeply staining granules or masses of questionable significance, 

 which are termed the tigroid bodies. Frequently, a region 



I/nplan fahon cone 



Fig. 4-4. — Neuro- 



Nucleus 



Fig. 45. 



Fig. 46. 



Fig. 45. — Nerve cell from ganglion of crayfish. {After Dollcy). 

 Fig. 46. — Neuroglia cells from nerve cord of earthworm, Eisenia rosea. 

 {After Schneider) . 



within the cytoplasm of the cell body directly continuous with 

 the cytoplasm of the axon is devoid of tigroid bodies. This 

 implantation cone, as it is sometimes called, is so marked in 



