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, Pl. VI. fig. 5; Pl. 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 
Raney 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 (Pl. 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 (aw) when viewed from 
the side, loses its angular elliptical shape, and has more or less the outline of an oyster- 
shell (Pl. VIII. figs. 4, 6, 8, 9; also Pl. 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 Hsoxv, 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 (Pl. VI. figs. 3, 4), though at certain 
points they become thickened, sensory cushions (new) being formed of large fusiform 
cells, which take a slightly radial disposition. An embryo of 7. 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 
(Pl. 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 (aw, 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 Anuelids, ¢., 
the stylets of the Nemerteans. LerEBoUuLLET 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). 6E 
