236 Annals Entomological Society of America [Vol. IV, 



tral side, while a central commissure crosses these to end in the 

 tangled mass of fibers on either side of the ganglion. Farther 

 along, these dorso-ventral bands a little one side of the middle 

 line do not cross the now larger central commissure, but run in 

 to it as do the other fibers from the ventral side, running 

 from the more deeply stained ventral mass already spoken of. 



Farther along and at the level of the next nerve, three com- 

 missures, a ventral, a dorsal and a median may be again recog- 

 nized while the fibers of the middle nerve both end in the lateral 

 portions of the fibrous mass and contribute to the three commis- 

 sures. In this level only a few scattering nerve cells were seen. 

 Beyond this a ventral, almost a lateral group appears again on 

 each side and fibers from these form a little arch about the now 

 smaller mass of darker staining fibers. On the mid-dorsal line 

 fibers from this arch and others from these cells also ramify 

 into all parts of the ventral portion of the ganglion. Along from 

 this the dorsal part comes to be separated into two separate 

 masses of longitudinal fibers of the connectives again. Far- 

 ther along the arch becomes in its dorsal portion fused into a 

 median commissure which soon disappears as the cleft between 

 the connectives becomes deeper and reaches way down to the 

 now small area of deeply staining substance which now forms 

 a ventral commissure. The ventral cell group has become more 

 lateral at this level and another large group has come in just 

 dorsal to it, but still only on the side. In the mid- ventral line 

 also, there has come in a small new group of cells. 



The last nerve trunk comes to be associated with this com- 

 missure of deeply staining fibers on the ventral side and farther 

 along fibers also pass freely into it from the lateral group of 

 cells which has been spoken of as coming in more dorsally, this 

 for a time remains distinct from the other more ventral groups. 



Along farther these cell groups unite to form a large thick 

 single lateral mass and from them more fibers run into the com- 

 missure of deeply staining fibers and "Punktsubstanz." 



Soon after this the commissure breaks through as the two 

 connective bundles separate, each with a little of the darkened 

 mass which soon disappears as do the cells of the ganglion. 



Although the above description is only a very general one, 

 it will be seen that the ganglion is more complicated than the 

 abdominal, but the general plan of arrangement and structure 

 is as in the abdominal region. The nerve cells as in the abdomi- 



