1 2 14 BULLETIN OF THE BUREAU OF FISHERIES. 



the occipital condyle and whose anterior ends diverge as they approximate the 

 regions of the orbits. These capsules form a part of the bony roof of the mouth 

 and are separated from this cavity by only a thin covering of mucous membrane. 

 In an adult fish the capsules are nearly an inch and a half (3.5 cm.) in length 

 and their longitudinal axes diverge from each other anteriorly at an angle of a 

 little over 40°. The internal ears lie partly in these capsules and partly in 

 the bony wall of the skull dorsal to the capsule (fig. 2). Each ear consists of a 

 sacculus with its appended lagena, and a utriculus and its semicircular canals. 



The sacculus is an elongated, thin-walled structure which lies in the cavity 

 of the bony capsule. It has the shape of a long flattened bean, and measures 

 in an adult fish a little over i '<( inches (3.5 cm.) in length by almost >< inch (i.i 

 cm.) in width. The walls of the sacculus are very thin and conform closely to 

 the shape of the inner surface of the bony capsule, to which they seem to be 

 molded. Much of the median wall of the sacculus is occupied by a large sensory 

 patch, the macula acustica sacculi, which receives the most considerable branch 

 of the eighth nerve. This patch is in the form of an elongated band of moder- 

 ate width extending lengthwise of the sacculus; its anterior end spreads out 

 into a very considerable oval area; its posterior end is marked by a smaller 

 expansion. The lateral wall of the sacculus is smooth and without special 

 nerve terminals. 



Each sacculus contains a large ear stone or otolith, the sagitta (i, 2, 3, pi. 

 cxxii), to use the term employed by Webb (1905), which almost completely fills 

 its cavity. In full-grown squeteagues these otoliths are conspicuous struc- 

 tures; they may measure i^ inches (3.2 cm.) in length by yi inch (i cm.) in 

 width. Their dry weight may exceed 25 grains (1.7 gm.). They are white 

 and hard and, excepting for a small organic residue, dissolve completely 

 with eff'ervescence in dilute acetic acid. They are chiefly carbonate of lime, 

 and their specific gravity, 2.84, is between those of the minerals calcite and 

 aragonite. Their concentric structure favors the belief that they are secretions 

 from the sacculus. Their lateral faces are irregularly concave (fig. i, C-F, 

 pi. cxxii) with a dorsal blade-like edge and a ventral blunt one. Posteriorly 

 they are roughly pointed; anteriorly they are flattened out into an almost 

 spatula-like ending. Their median faces (fig. i, A-B) are relatively smooth 

 with a slightly depressed figure on them corresponding to the form of the 

 macula acustica sacculi, against which they are well adapted for resting lightly. 



At the posterior end of the sacculus is a small triangular pocket, the lagena, 

 which contains a flattened otolith, the asteriscus, and a single sensory patch, the 

 papilla acustica lagenae, to which a branch of the eighth nerve is distributed. 



Although the sacculus communicates freely with the lagena, it does not 

 connect with the utriculus. A careful search in fresh and in well-preserved 

 material for a communication between these two parts failed to reveal the least 



