NOTES ON HISTOLOGY OF LINGULA ANATINA. 19 



posterior end in common with the above band. The greater part 

 of the ventral face, the entire anterior face and a small part of 

 the dorsal face of the otocyst is free and coated with a layer of 

 longitudinal muscle which attains a considerable thickness at the 

 anterior end. The otocyst itself is composed of an external 

 layer of the supporting substance and an inner sac formed by a 

 thick epithelium. The supporting layer is of different thickness 

 at different places : it is thickest at the posterior edge and on 

 the median and lateral sides, while in other parts it remains thin. 

 Interior to the supporting layer there is a very thick epithelial 

 sac, composed of tall columnar cells with nuclei near their bases 

 and placed at several different levels. The nuclei are of a spindle 

 shape, and have a great affinity for stains. The epithelial cells 

 are highest along the edge formed by the meeting of the two 

 surfaces of the lens-shape. The cells are throughout of the same 

 structure and no other elements occur among them. At the tip 

 of these cells feeing toward the cavity there is no indication of 

 the cuticula formation, but there fine rod-like granules are seen, 

 which with a high degree of certainty are to be regarded as the 

 basal pieces of cilia, indicating that the inner cavity of the otocyst 

 was covered with cilia, although in fixed specimens no cilia could 

 be detected. In the cavity there are found some thirty spherical 

 otoliths, varying greatly in diameter, the largest measuring 3-4/A 

 They are compact, highly refractive and take a somewhat deep 

 hematoxylin stain which proves that they are organic in com- 

 position and hence not introduced from without, but secreted 

 from the walls. Along the margins of the lenticular vesicle 

 there is left a ring-shaped space filled with granular substance 

 and in one region a few muscle fibres. The former is no doubt 

 nervous in nature, but I must confess that but little is known 



