US 



[ou rnal oi Entomology and Zoology 



the libers and fibrils more intimately related in all parts ol the 

 thickness oi the nerve strands. In cross section the libers and 

 fibrils in .i \ be followed straight in more easil) than in longitudinal 

 sections, where there is evident a decided longitudinal disposition 

 of the libers and fibrils. Cells, especially in the smaller sea-urchin, 

 are very numerous and the fibers ov fibrils \ er\ small. 



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

 is narrow, with onl\ several layers of cells. Fig. 5 is a section ol 

 one oi 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. I here are mam 

 line fibrils and possibl) in some cases libers made up oi fibrils. 

 Main cells in the larger species seem more complex than hi-polar 

 forms and some true nerve cells have migrated to the area oi libers 

 .\i\d fibrils. Some oi these show fibrillae joining the cytoplasm. 

 Some oi 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 main others are multi-polar in the 

 general cell area. There are main cross hues of libers a\\<\ fibrils 

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

 cate than in starfish. 



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

 species ol sea-urchins is compared with starfish, the\ differ as much 

 from each oilier i i general appearance of the sections as the) differ 

 I rom starfish. 



REFERENCES 



. /•:. is:: 



Etudes generates sur le systeme nerveux, com. a 1 "Hist . du syst. 

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

 Dc/a( =.//-./ 1903 



frail de Zool. Concrete, t. 3. I es eehinodemis, 

 Krohu, /. 1S41 



Neber die anordnung tics Nervensystems der Echiniden unci Holo- 

 thurien im Allgemeinen Mviller Arch. An.u.. vol, of IS41. 

 Vi ../. 1854 



N ier den Han der Echinodermen, Abh. Akad. \\ iss.. Berlin. 

 tcher, R. 1876 



B< • ■ anatomie der Echinodermen. Jen,/. N , vol. 10. 

 I' nl p :.;>!, ./. 1866 



I econs sur la phvsiologie generate et comparee du svsteme nerveux. 

 Pai s 



..'.■./ ... - ' i . . . 



