181 
into the epidermis. The nerve supply to the otocyst is 
derived from the cesophageal connectives. Around the 
point of origin of this nerve and along its course are 
numerous large ganglion cells with vesicular nuclei. The 
nerve comes into contact with the otocyst at the point 
where the tube leads off to the exterior and is intimately 
related to both structures as it provides them with a 
sheath of nervous elements. The nervous sheath lies 
below the epithelium of the otocyst and tube, among the 
nerve fibres occur scattered fusiform or stellate cells. 
The otocyst, in life, contains a fluid of a somewhat 
viscous nature which consists of a secretion of the walls 
of the otocyst and its tube mixed with sea water. It also 
contains numerous otoliths in the form of foreign bodies 
such as quartz grains, portions of spicules, frustules of 
diatoms, &c. In some specimens the original otoliths, 
which were irregular in shape, have been covered by layer 
upon layer of secreted substance of chitinoid nature, the 
resultant otoliths having rounded outlines. This condi- 
tion is met with in moderately old specimens (130 to 250 
mm. long) in which also the tube of the otocyst has 
become closed either by apposition of its walls or by the 
blocking of the lumen by a granular substance secreted by 
the gland cells in the wall of the tube (fig. 50). That 
this rounded character of the otoliths depends upon the 
closure of the tube is shown by the fact that in other 
specimens (about 170 mm. long), in which the lumen of 
the tube is a fair-sized slit, the otoliths are irregular and 
uncoated foreign bodies. In most young specimens the 
otoliths consist of irregular bodies which are almost naked, 
i.e., they have either no secreted covering or else it is ¢ 
mere film the presence of which is indicated by its staining 
with hematoxylin. 
Whenever the otocyst is examined fresh under the 
