234 Annals Entomological Society of America [Vol. IV, 



in the cephalic portion of the ganglion. Other than these 

 differences, there were no essential ones between these nerve 

 centers and those of the abdominal region. 



In regard to the arrangement of cells as shown by methylene 

 blue, it was found that the lower ventral and lateral regions 

 had the greatest number, great masses of them, with many 

 more cells than in the smaller ganglia. For the most part 

 similar arrangements of individual ribers were seen. Nerve 

 cells sending fibers directly into motor trunks, cells of medium 

 or rather small size, were observed, but these were few in num- 

 ber. Most of the cells seen had their processes running into 

 the "punktsubstanz" of the ganglion. Large and smaller asso- 

 ciation cells were found as in the lower regions and of various 

 sorts such as already described for them, some at the surface of 

 the ganglion other at the edges of the "punktsubstanz." 



Between the third and second and the second and first 

 thoracic ganglion, there are branches off from the connectives, 

 a pair between each of these, and between the subesophageal 

 and the first thoracic there are two pairs. The upper of these 

 last were not so well stained in any of the preparations but all 

 of the others were quite well colored and found to be motor. 

 These branches when studied as to their composition did not 

 differ much from each other and in each one, fibers could be 

 seen descending to run out the nerve trunk from the ganglion 

 next above and also from the ganglion below. These two 

 tracts of fibers entering the lateral trunks were clear and dis- 

 tinct from each other for quite a distance into the nerve trunk. 

 (Fig. 4). 



THORACIC GANGLION IN SECTION. 



(Plate XV, Figs. 1-4.) 



The internal structure of the thoracic ganglia is much more 

 complicated than the abdominal, due to the fact that the larger 

 branches from the more numerous nerve cells are more inti- 

 mately woven together, and it was practically impossible to 

 follow commissures or tracts very far except in a very general 

 way. However, a general description as detailed as seems 

 necessary will be given of one of the thoracic ganglia, the first. 



From above the connectives which enter as in the abdom- 

 inal ganglia are in every way similar. Not many cells are seen 

 scattered in the upper part of the ganglion, then two large 



