DEVELOPMENT AND LIFE-HISTORIES OF TELEOSTEAN FISHES. 761 



noticed that, as the auditory vesicles elongate, "a mass of yellowish granules" appeared 

 in them prior to the formation of the true otoliths (No. 93, p. 529). The contents of the 

 otocysts seem, however, to be clear, homogeneous, and without granules in our forms, but 

 usually before the end of the first week, and within twenty-four hours after the lumen 

 in each is defined, two minute calcareous bodies appear on the floor, usually towards 

 each extremity of the longer axis of the otocyst (oto, PI. VI. fig. 5; PI. XII. figs. 1-5). 

 These otoliths have the appearance of two very small dense grains, and are, as Dr 

 Carpenter remarks (No. 37), similar in character and mode of formation to the concre- 

 tionary spheroids common in the urine of the horse, the integument of the shrimp, and 

 other forms. It is well known that when a solution of lime-salt in gum-arabic is slowly 

 decomposed, carbonate of lime is deposited in spheroidal concretions. Sometimes, as Mr 

 Rainey found, two of these will unite in dumb-bell form, and occasionally a number will 

 unite in the form of a mulberry (No. 126, p. 19). # The walls of each otocyst are com- 

 posed of columnar or rather spindle-shaped cells, and at first over much of their surface 

 several layers are superposed (PI. VI. figs. 3, 4). Subsequent changes, however, not 

 only affect the thickness of the walls, and cause them to thin out, but alter their contour. 

 Moreover, being pressed in, from above, anteriorly, the otocyst (au) when viewed from 

 the side, loses its angular elliptical shape, and has more or less the outline of an oyster- 

 shell (PI. VIII. figs. 4, 6, 8, 9; also PI. XII. figs. 1-4, 7). A ridge also appears on the 

 floor, caused apparently by some of the internal nervous tissue being aggregated along 

 the shorter axis of the capsule (PI. VIII. fig. 8). In Esox, about the time the cardiac 

 chamber is formed, and the embryo rises erect upon the yolk, the otocysts, according 

 to Lereboullet, become more transparent, and have a thick investment like cartilage 

 (No. 93, p. 529). No such investment appears in our forms until very much later, the 

 walls retaining their original cellular structure (PI. VI. figs. 3, 4), though at certain 

 points they become thickened, sensory cushions (neu) being formed of large fusiform 

 cells, which take a 'slightly radial disposition. An embryo of T. gurnardus, six days 

 after hatching, shows three such nervous aggregations provided with erect motionless 

 cilia or palpocils. That situated upon the floor is by far the largest, but it may vary 

 somewhat in outline as well as position. The remaining two are anterior and posterior 

 (PI. VI. fig. 2). In one specimen, viz., the example figured, a dorsal hernia (x) or 

 process of the cellular wall occurred. A long trumpet-shaped tunnel (can) passed 

 anteriorly and superiorly, the inner end being faintly granular and botryoidal in appear- 

 ance from the irregularity of its cells. In some forms the ears become so enormously 

 developed that they may nearly meet in the middle dorsal line, or may, as Parker 

 describes in Salmo, actually overlap the posterior border of the eyes (No. 117, p. 113). 

 In the gunnel (au, PL XIII. figs. 5-7) they are certainly very much larger at a com- 

 paratively early stage than in any other form reared at St Andrews, and they may 



* A still more striking example of definite concretions in a clear fluid is that afforded by certain Annelids, e.g., 

 the stylets of the Nemerteans. Lereboullet proved their calcareous nature in fishes ; he says — "Treated with acid 

 they effervesce and disappear. No membrane is left, or it is too thin to distinguish " (No. 93, p. 633). 



VOL. XXXV. PART III. (NO. 19). 6 E 



