Nerve Cells of Tarantula 



WILLIAM A. HILTON 



G. Saint Eemy '90 and others have indicated at least two sizes 

 of cells in the nervous systems of spiders. In tarantula there 

 are numerous cells of small size and fewer of a larger sort. The 

 functional nerve elements may be told from the others by their 

 rather clear nuclei which contain prominent nucleoli. The large 

 cell-bodies as compared with the size of the nuclei are also char- 

 acteristic. No neuroblasts were clearly recognized in the adult 

 spider. Two types of elements were seen which were thought to 

 be connective in their nature, or neuroglia cells. In one kind of 

 these the nuclei were rather clear, the cells widely scattered, but 

 often partly joined togetlier Ijy their long slender processes. 

 Some of these were found in the fibrous portion of the ganglion. 

 In the other type of supportive element the cells are massed 

 together in certain regions, the nuclei are filled with granules of 

 chromatin and fine strands from the cytoplasm extend between 

 the adjoining cells and penetrate into the fibrous area. These 

 two t^iies of elements form a framework or reticulum for the 

 cells and fibers of the nervous system (Fig. 1, D and E). 



The smaller nerve cells seem to be rather simple for the most 

 part. They appear to be unipolar with a large process directed 

 towards the central filirous mass of the ganglion. The nuclei 

 of these are large with large nucleoli which contain one or more 

 refractive spots. Fibrils are not so easily determined as in 

 larger cells, but the nerve processes seem to be composed of 

 many fine fibrills. Little was learned about other points in the 

 finer structure of these cells, Init in jireparations fixed in Flem- 

 ming's fluid there were numerous dark masses which were often 

 seen. These were usually found in the cytoplasm on the oppo- 

 site side of the cell from the nerve process. In appearance these 

 resembled blackened fat particles (Fig. 1, C). 



The larger nerve cells were found grouped together or scat- 

 tered about in the more ventral regions of the nervous system ; 

 some were found in the supraesophageal region, on the lateral 



