A PRELIMINARY STUDY OF THE CENTRAL 

 NERVOUS SYSTEM OF SPIDERS 



WILLIAM A. HILTON 



It is surprising how little work has been done on the central nervous 

 system of spiders. Most that we know of this organ in arachnids is due to 

 earlier investigators. There are the papers of Trevianus in 1832, Brandt in 

 1840, Grube in 1842. Then there is the work of Schimkewitsch in 1884. 

 The first extensive account of the central nervous system studied by modern 

 methods is by St. Remy in 1890, where a number of brains or supKBSopha- 

 geal ganglia are considered. There are also the numerous papers by Patten 

 on Liuuilus and his recent book on the origin of vertebrates. 



The following preliminary study has been made from dissections and 

 serial sections from the nervous systems of members of the family Avicu- 

 larioidea. Figure 261 and Figure 262 are drawn from tarantula Eury- 

 phelma californicum. Two chief masses of the central nervous system are 

 easily recognized in the cephalothorax. The part corresponding to the sub- 

 esophageal, thoracic and abdominal ganglia is larger and as shown in the 

 figures has five pairs of large nerves given off from it and one unpaired 

 nerve in the caudal region which goes to the abdomen and branches a number 

 of times. The lower four pairs of nerves are slightly larger than the 

 abdominal and these go to the legs. Just in front of the first pair of leg 

 nerves is the slightly smaller one on each side of the ganglion; this runs 

 into the palpus. Fibers from all of these nerves penetrate more or less 

 deeply into the ganglion and each one is intimately associated with numerous 

 large and smaller nerve cells. The cells are for the most part ventral in 

 position and fibers from them and from other parts form an intricate net- 

 work in the central portion of the ganglion, all indications of special areas 

 of cells and fibers being lost at such points. 



The five pairs of nerves and the caudal unpaired one have to some 

 degree the appearance of being made up of several portions as seen in the 

 gross structure. The distribution of these nerves so far as could be deter- 

 mined without special stains, was such as to indicate that they were made up 

 of afferent and efferent components. 



Figure 2()2, A, shows some of the main brandies of a nerve as it passes 

 ilnwii a h'g. Petrunkevitch, '09, has described the nuiscles in the legs of 

 i'holcus, but a general examination of the appendages of tarantula has 

 shown more complex contlitions. The muscles will not be considered 

 especially at this time. In the first four joints of the front leg shown in the 

 diagram, the muscles are more distinct and when the nerve is exposed from 

 above, branches may be seen as sliown in the figure. The nerve in this part 

 of its course runs nearer the upper side of the leg so that most of the 

 muscles shown are extensors. In the last three joints, the main nerve trunk 



