368 



EVENINGS AT THE MICROSCOPE. 



minute, without any bulbs;— from four to seven be- 

 tween every two of the primary ones. We won't 

 mind these, but bringing the margin itself into focus, 

 and moving it along the stage horizontally, we pres- 

 ently see one and another singular organs. They are 

 eight in all, two being placed, but irregularly, in each 

 of the four quadratures of the circle formed by the ra- 

 diating canals. 



There are auditory vesicles, or organs of hearing, 

 very closely similar to those which we see imbedded 

 in the bosom of the Snail and other MoUusca. Plere 

 they are comparatively large, and unusually well 



OTOLITnES OF TnATJJIANTIAS. 



furnished. Each is a semi-oval enlargement of the 

 flesh of the margin, in close connexion with the walls 

 of the marginal canal, hollowed so as to inclose a 

 capacious cavity, in which are placed a considerable 

 number — ^from thirty to fifty in this individual — of 

 otolithes, or spheres of solid, transparent, highly re- 

 fractive substance. They are arranged in a double line, 

 forming a crescent, and those which are nearest the 

 centre are longer than those towards the extremities 

 of the line. I believe some observers have seen oscil- 



