1917 Pomona College Journal of Entomology and Zoology, Vol. IX, No. 2, June 



The Central Nervous System of the 

 Amphipod Orchestia 



William A. Hilton 



Numerous specimens of Orchestia traskiana Stim. were collected 

 at Laguna Beach. Some were preserved whole, from others the 

 central nervous system was studied in position or removed in one 

 piece and stained and sectioned or mounted whole. For whole 

 mounts some carmine stain or a light hermatoxylin coloration 

 seemed best. For sections a copper hematoxylin was used with 

 good results. 



The brain occupies the forward portion of the head with large 

 branches or lobes to the compound eyes which are somewhat dorsal 

 and caudal from the brain as it lies in the head. Large nerves to 

 the antenna 1 and smaller ones to the antennules cannot be seen 

 from above as they run from near the connectives in a more ventral 

 and caudal region. The brain is held in place by a band of tissue 

 which perforates it near the center. In the figure the brain is not 

 shown in the normal position. It is pulled out so as to show its 

 parts better. The connectives join the rather small first ganglion, 

 running almost ventrally when not displaced. Including this gang- 

 lion there are eight large thoracic ganglia and four small abdominal 

 centers, the last of which is a little larger than the other three. 



In whole mounts the brain does not show well. The ventral 

 ganglia from surface views are found to contain a coating of large 

 and small cells, especially on the ventral sides. Some of these are 

 shown in the figures, which give views of a large and a smaller 

 ganglion at one optical section. There are several layers of cells 

 and both large and small are numerous, the latter of several sizes 

 very numerous. The general position of some of the larger cells is 

 shown in the figures. 



In section the brain is found to lie chiefly composed of fibers and 

 fibrils. Large strands of fibers run long distances and connect wide- 

 ly separated regions. \o very large cells were found in the brain, 

 such as found in the ventral ganglia, anil no very marked central 

 region of the brain was clearly seen. The cells as compared with 



