72. JOUENAL OF ENTOMOLOGY AND ZOOLOGY 



Staining masses so characteristic of many arthropods. In no place 

 is the fibrous mass of the brain or ganglia of great complexity. 

 Fibers for the most part run in straight pathways, many connect 

 the brain with lower levels, but possibly less than are usually found 

 because the connectives with the brain are rather narrow. More 

 or less continuous cell masses inclose the brain and upper ganglia. 

 These cells are massed, there are several sizes and the staining re- 

 actions differ. In places some cells take a much deeper color. 



There are not many indications of cross connections between 

 right and left halves in the lower portion of the nervous system. 



One of the most remarkable features of the brain is the failure 

 of the more forward lateral portions to unite across the middle 

 line. Back from the center fusion takes place above, but not at the 

 dorsal surface. For a short distance three parts of the brain may 

 be distinguished although they are largely fused with each other. 

 Back of this the antennal lobes become distinctly separate, and at 

 last end in the narrow connectives which run to the ventral ganglia. 



The eleven thoracic ganglia may be determined by the position 

 of the appendages of this region and to some degree also by the 

 location of the nerve cell groups. The six abdominal ganglia are 

 well marked from each other and towards the last the right and 

 left connectives may be determined for the first time in the ventral 

 chain. 



Another interesting condition of the nervous system is found in 

 the brain. A slight cavity remains for a time between the two 

 lateral halves of the upper part of the brain in a dorsal position. 

 This space is shut in above by a small mass or line of cells which 

 may not be nerve cells, although they are joined with the brain. 

 It seems as though the two lateral halves of the brain came to- 

 gether leaving a cavity between which they at last bridged over 

 dorsally by the growth of adjacent parts. This suggests a similar 

 formation of a cavity in the central nervous system of vertebrates 

 at an early time. 



SUMMARY 



1. The central nervous system consists of the brain of three 

 fused ganglia, the ventral chain of about eleven centers and the 

 six abdominal ganglia. 



