198 HANSFORD MACCURDY 



in these experiments. The fifth abdominal ganglion was selected 

 as the most suitable for study, because its position rendered it 

 accessible for operative purposes and its structure appeared rea- 

 sonably simple as to the number and distribution of the large 

 ganglion cells. In this ganglion, in its normal condition, are 

 found a few relatively large ganglion cells whose positions are 

 fairly constant and whose identity can be determined with cer- 

 tainty, at least in most cases. Of these large cells a few lie well 

 forward in the ganglion, near its ventro-lateral surfaces, forming a 

 group on each side of the ventral line. In each of these groups 

 there are a few easily recognized cells larger than the others. 

 These lie in the anterior third of the ganglion. Immediately pos- 

 terior to each anterior group of cells, though not distinctly sepa- 

 rated from them, is another group of cells, which lies for the most 

 part beneath the roots of the large lateral nerves. In this region 

 are three or four nerve cells which are usually the largest found 

 anywhere in the ganglion. A transverse section passing through 

 the roots of the lateral nerves usually cuts through one or more 

 of these large ganglion cells. In the section, these cells lie near 

 the ventral surface of the ganglion and to the right or left. It is 

 thus seen that the identification of the particular cells is reasonably 

 certain. Posterior to the group of cells just described, and closely 

 connected with it by the smaller cells, lie the remaining large gan- 

 glion cells which form the posterior part of the ganglion. As 

 in the other parts of the ganglion, the cells of the posterior group 

 vary in diameter, and individual cells may be identified by their 

 position as well as by their size. It is to the large ganglion cells 

 in the positions which have just been pointed out that attention 

 is particularly directed later. 



The smaller cells were less suited to the requirements of the 

 experiments than those just described because of the difficulty 

 with which their finer structure could be determined. Of the other 

 abdominal ganglia only the fourth and sixth need be mentioned. 

 While the fourth ganglion was not studied as fully as the fifth, 

 it was clear that the large cells were arranged in it in much the 

 same way as in the fifth, and that the disappearance of any cell 

 or cells from this ganglion could be easily recognized. The sixth 



