148 Journal of Entomology and Zoology 



the fibers and fibrils more intimately related in all parts of the 

 thickness of the nerve strands. In cross section the fibers and 

 fibrils may be followed straight in more easily than in longitudinal 

 sections, where there is evident a decided longitudinal disposition 

 of the fibers and fibrils. Cells, especially In the smaller sea-urchin, 

 are very numerous and the fibers or fibrils very small. 



In the larger species the radial nerve is broad, but the cell area 

 is narrow, with only several layers of cells. Fig. 5 is a section of 

 one of the nerve strands from the smaller species. Fig. 6 is from 

 the larger species. Both figures are drawn to the same scale and 

 enlarged more than the other drawings. As the cells are larger in 

 the larger species the fibers seem to show better. There are many 

 fine fibrils and possibly in some cases fibers made up of fibrils. 

 Many cells in the larger species seem more complex than bi-polar 

 forms and some true nerve cells have migrated to the area of fibers 

 and fibrils. Some of these show fibrillae joining the cytoplasm. 

 Some of the cells in the fibrous area especially seem to be neuroglia 

 cells, or at least are not nerve cells. Some multi-polar cells are 

 shown in the figure, probably many others are multi-polar in the 

 general cell area. There are many cross lines of fibers and fibrils 

 in the whole thickness, but the massing of fine strands is more intri- 

 cate than in starfish. 



As to the general character of the nervous systems of these two 

 species of sea-urchins is compared with starfish, they differ as much 

 from each other in general appearance of the sections as they differ 

 from starfish. 



REFERENCES 



Baudclot, E. 1872 



Etudes generales sur le systenie nei\eu\-, cont. a I'hist. du syst. 

 new. des echinodermes. Arch. Zool. exp. vol. 1. 

 Dehige et Herotiard 190.3 



Trail de Zool. Concrete, t. ?>. Les echinoderms. 



Kroh,i,A. 1841 



Neber die anordnung des Nervens\ stems der Echiniden und Holo- 

 tluirien im AUgemeinen Miiller Arch. Anat., vol. of 1841. 



Midler, J. 1854 



Sfeber den Ban der Echinodermen. Abli. Akad. Wiss., Berlin. 



Teiischer, R. 1876 



Beitriige zur anatomie iler Echinodermen. Jen, Zeit. Nat., vol. 10. 



f'ulpidii, A. 1866 



Legons sur la pinsiologie generale et comparee du svsteme nerveux. 

 Paris. 



( Criiitnl/iilion jriitii llic Zdoliitfual Lahdiiitoiy of I'otiiriiia Culligt) 



