762 J. H. ASH WORTH. 



marked (1001^ p. 178) ou the small size of the opening 

 from the tube into the otocyst iu A.assimilis, and con- 

 sidered that this was connected with the furni ot" the 

 otoliths. I had pi-evionsly arrived at the conclusion that 

 their shape was due to the closure of the lumen of the tube^ 

 and had examined a number of otocysts of A. marina to 

 obtain further evidence ou this question. The anterior ends 

 of nine specimens of the latter species have been sectioned, 

 and show considerable differences in the character of their 

 otoliths. Six of the specimens are comparatively young (from 

 about 17 to 65 mm. in length), and their otoliths are irregular 

 foreign bodies such as quartz-grains, portions of spicules, 

 friistules of diatoms, etc., which are almost naked, i. e. they 

 have either no secreted covering, or else it is a mere film, the 

 presence of which is indicated by its staining with htema- 

 toxylin. Of the remaining three older specimens, one, which 

 is about 170 mm. long, has irregular otoliths like those 

 described above, but in the other two, which are about 130 

 and 250 mm. long respectively, the otoliths have quite a 

 different appearance. They were at first irregular, but the 

 original particles have been covered by Vdyev upon layer of 

 secreted substance, and the resultant otoliths have rounded 

 outlines (see fig. 10). The tubes of these two pairs of 

 otocysts are found to be practically closed along almost their 

 Avliole length, either by apposition of the walls or by the 

 blocking of the lumen by a granular substance secreted l)y 

 the gland-celis in the wall of the tube. In each case the 

 walls of the tube are so closely apposed that the lumen along 

 the greater })art of its length is reduced to a slit not more 

 than o or 4 /.i across, and even this space is occupied by a 

 thin band of the secreted substance mentioned above, thus 

 effectually closing the passage. The variation in the nature 

 ot tiie otoliths is probably dej)endent on the condition of the 

 tube. At any rate, it is interesting to note that in the large 

 specimen (1 70 mm. longj with irregular otoliths mentioned 

 aljove, the luinin of the tube, as seen in section, is a fair-si/ed 

 slit, and i.s not encroached upon to any extent by secretion 



