7\NAT0]\IY OF AEMNICOLA ASSi:\r[LTS. 753 



The opcninpf is close to the point of origin of the oesophageal 

 connective^ i.e. nt the dorsal end of the nietastomial groove, 

 so that it is more dorsally situated than the corresponding- 

 opening in A. marina. The lumen of the tube is small^ 

 and in two of the foui- examined is almost obliterated along 

 part of its length by approximation of the walls. In three of 

 the tubes there are fine paiticles of foreign matter at one or 

 more points. The otocyst and tube are lined with a cuticle 

 about 3 /< in thickness. The epithelial wall of tlie otocyst is 

 comparatively thin (30 to 40 //). The sense cells are not 

 easily distinguishable, at first sight, from the supporting cells, 

 but in one series of sections they may be distinguished by 

 the presence of neuro-fibrilla? in the former. Each sense cell 

 is seen to be traversed by a single fine fibril, which terminates 

 immediately below the cuticle. These cells and fibrillse are 

 especially abundant in the wall of the otocyst near the 

 entrance of the tube, and they are also present in the 

 adjacent part of the tube. Below the epithelium is the 

 nervous sheath, among the fibres of which occur scattered 

 fusiform or stellate cells. The nerve-supply to the otocyst is 

 derived from the tesophageal connectives (see above, p. 750). 

 'Jlie otocyst contains the coagulated remains of the fluid with 

 which it was filled in life. Among this coaguhim are 

 numerous minute spherical deeply staining granules, whicii 

 are probably secreted by some of the cells in the wall of the 

 otocyst (fig. 13), There are about forty or fifty otoliths in 

 each otocyst; they are usuallj^ spherical, but a few are oval, 

 and some are irregular, but have a rounded outline. They 

 neai'ly all show concentric markings indicating the method 

 of their formation by deposition of layer upon layer of a 

 secretion produced by cells in the wall of the otocyst. 'I'lie 

 largest otoliths are 35 fx to 45 fj. in diameter. In the centre 

 of a few of them there is a minute refringent body, evidently 

 of foreign origin, forming the nucleus around which the 

 secreted matter has been deposited. Besides the contents 

 already named, there are in the otocyst several deeply 

 staining bodies varying in size from the minute granules 



