430 WILLIAM A. HILTON 



by two commissures. The number of pairs of ganglia depends 

 largely upon the degree of segmentation of the body of the 

 crustacean. 



The fortunate opportunity to obtain a large number of living 

 Crustacea gave much of the material for this study. Methylen 

 blue was tried without success as long as the animals could be 

 obtained alive, afterwards dissections and sections were made 

 from preserved material. Mercuric chloride fixation seemed most 

 advantageous. The whole nervous system was dissected out 

 and lightly stained with a carmine solution or a clear alcoholic 

 hematoxylin. Later the specimens were mounted in balsam. 

 This method had many advantages because all parts of the simple 

 nervous system could be seen at once The cells and fibers were 

 not numerous enough to greatly interfere with the clearness of 

 the preparations. Especially was it noted that the cells were 

 not distorted as is usually the result after sectioning methods. 

 Some serial sections of whole animals or parts were prepared 

 for comparison. 



GENERAL FORM OF THE GANGLIA 



In the forms studied, in general no new features of external 

 morphology were noted. Artemia and Branchipus were practi- 

 cally the same except for the larger size of the nervous system in 

 Branchipus. In these the brain has connected with it laterally 

 the two large optic nerves which expand into the optic ganglia 

 (not shown in figures). The antennulary nerves come off from 

 the brain where it joins the esophageal connectives and the 

 larger antennal nerves come off a little farther down From 

 the cephalic side of the brain a median nerve is connected to the 

 median eye and two pairs of nerves lateral to this supply upper 

 parts of the head. 



The first three pairs of ventral ganglia supplying the head, 

 mouth parts and upper portions of the body are much smaller 

 than the more caudal ganglia. The last ganglion or pair of 

 nearly fused ganglia change somewhat as they terminate in 

 abdominal branches (figs. 1 and 2). 



