262 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



microscope, either in situ in young transparent specimens 

 or after being rapidly dissected out, the otoliths exhibit a 

 peculiar quivering and rotatory movement. This motion 

 is probably due to the action of the cilia in the entrance 

 to the tube which leads to the exterior. 



The otocyst does not appear to be an organ of hearing 

 as the animal takes no notice of even loud sounds made in 

 its immediate vicinity. It is more probably an organ 

 for enabling the animal to appreciate its position in the 

 sand or in the water and thereby to direct its movements. 



The Nuchal Organ (figs. 5, 34 and 47) is a U-shaped 

 ciliated groove formed by an invagination of the epidermis 

 of the posterior part of the prostomium. The epithelium 

 of the organ is composed of columnar cells, some of which 

 are distinguished as sense cells by the presence of neuro- 

 fibrillse. The intervening supporting cells are rather 

 stouter, and many of them are ciliated. In old specimens 

 pigment granules are deposited in many of the cells. 

 Beneath the epithelium there is a layer of nervous 

 elements in connection with the posterior brain lobes. 

 The organ probably has an olfactory function. 



The Eyes (figs. 47 and 48). — Two to five eyes, one of 

 which (the oldest) is larger than the others, are present on 

 each side of the prostomium in post-larval stages (figs. 

 56 and 59). Only in very young specimens from the sand 

 are they visible externally. They m.aj be found in sections 

 of specimens up to 70 mm. long by which time they have 

 sunk below the epidermis and have become imbedded in 

 the mass of ganglion cells on the dorsal surface of the 

 anterior cerebral lobes just in front of their point of union. 

 They are difficult to find in older specimens owing to the 

 increase of pigment in the prostomium, and they are 

 apparently wanting in some old specimens. 



The eyes are very simple in structure. Each is com- 



