242 Annals Entomological Society of America [Vol. IV, 



tance cephalad of this point the ventral mass disappears and the 

 lateral halves of the general mass of fibers becomes distinguish- 

 able once more as the upper region of the ganglion is reached. 

 At this upper region, lateral cells are no longer seen, there is 

 however, a small group ventrally placed, either side of the 

 middle line and a small dorso-median mass. Fibers sent in 

 from these curve up to run into the crus which may also at this 

 level be seen to receive fibers from the middle and opposite 

 parts of the ganglion by the way of a group of fibers just one 

 side of the middle line and a group running from the center of 

 the lateral central mass. 



Just beyond this last level at the place where the maxillary 

 branch enters, a little group of nerve cells comes in between it 

 and the crus. Fibers from this large maxillary "nerve run into 

 the crus, into the central and ventral portion of the ganglion and 

 apparently across to the other side, while many of its fibers are 

 lost in the deeper staining central masses. 



Farther along the ventral cells become much more abundant, 

 a wedge shaped group 0-7 layers thick with a few large cells. 

 A few cells come in on the mid-dorsal line and some come in 

 latero-ventrally just above where the maxillary nerve joins the 

 ganglion, and some of these cells seem to contribute directly to 

 the nerve. 



The large mandibular nerve joins the ganglion on its upper 

 border, fibers come to it from ventral and dorsal sides of the 

 ganglion and connections with the darker fiber masses in the 

 center can be traced. Cells are now in masses both dorsally 

 and ventrally as the cephalic end of the ganglion is approached 

 and some of these at least seem to contribute directly to the 

 nerve. 



The above description is a very general one, only the main 

 features of structure and arrangement were spoken of. The 

 complexity of the ganglion is such that a general summary of it 

 follows : 



(a) Cells 



The cells at various levels differ greatly. Beginning at the 

 caudal end and passing forward there might be recognized 

 about three main dorsal cell groups one after another which 

 fuse and separate from each other at various levels. The median 

 ventral cells are at first also separated from the other groups 



