NERVOUS SYSTEM OF CRUSTACEA 435 



In each ganglion of each side the cells are arranged in a char- 

 acteristic manner. In all the middle body ganglia the ventro- 

 mesal cell group is less marked than the ventro-lateral. The 

 outer portion of the ventral-lateral group often has a number of 

 large cells similar to those in the other group. The larger cells 

 in most cases represent those that send their fibers longer dis- 

 tances, but they often have more than one branch and the exter- 

 nal and internal mass of fibrillae connected to them seems more 

 complex than on smaller cells. In some cases the larger cells 

 seemed to have their cytoplasm fused, but most of the cells, 

 although near each other, had their cell bodies distinct. Nerve 

 fibrillae are evident between and in cells, although some of the 

 largest cells have one or two large fibers which leave or enter the 

 cells. Some cells of apparently the same type seem to have no 

 very large branch, but fibrillae enter and leave the cell. Many 

 large cells seem to be penetrated on all sides by numerous fibril- 

 lae, or if fibrillae do not all penetrate they are closely related to 

 all the peripheral parts of the cell body. 



Cells of varying numbers are found in the commissures, these 

 are chiefly medium or small cells and some at least are nerve 

 cells. The number of cells in the ganglia was possible to de- 

 termine quite well from surface preparations and some compari- 

 sons were made between Artemia and Branchipus. The larger 

 species has not only the larger nerve cells, but the larger number 

 of nerve cells. The number of cells in corresponding ganglia 

 was found to be less in the smaller animals. The average 

 number of cells in the middle ventral ganglia on each side ran 

 from 130 to 204 in Branchipus, while Artemia had from 120 to 

 160 cells in each lateral ganglion. The number of cells in the 

 intermediate ganglia of a number of specimens was counted and, 

 although the count cannot be considered absolute because of 



Figs. 5 and 6 Sections through the abdominal ganglia of Branchipus. The 

 dorsal side is to the top of the page. X 75. 



Fig. 7 Brain of Branchipus from a surface preparation. The cephalic side 

 is to the top. X75. 



Fig. 8 Upper ventral ganglia of Branchipus, surface view. The cephalic 

 end is at the top. X 75. 



