1908.| Structure and Relationships of the Labyrinth. Sly 
or, if present, the quantity must be so small in amount that it is invisible to 
the eye even when the organ is magnified to five or six times its natural size. 
It is not possible to give here a satisfactory description of the perilymph 
recess and round window in the penguin, since in the specimen obtained by 
the writer the lower portion of the cavity was broken off, carrying with it 
the round window, if that opening exists in this bird. The destruction of the 
lower portion of the perilymph recess, however, has had one advantage: it 
shows clearly the large oval opening, 0.0., between that cavity and the scala 
tympani of the cochlea. 
On the upper surface of the perilymph recess in the labyrinth of the 
penguin there is an opening, d@.p., in the wall of the cavity. This dehiscence 
is oval in shape and occupies the position of the aqueductus perilymphaticus 
(or aqueduct of the cochlea as it is sometimes termed) in other birds, such as 
the ostrich, emu, tinamou, etc. It corresponds exactly to the opening which 
is found in the same position in the monitor, and permits of intermingling 
of the perilymph with the cerebro-spinal fluid. In other words, the penguin 
does not possess an aqueductus perilymphaticus in the proper sense of the 
term, the channel being represented merely by an oval opening. 
The Membranous Labyrinth of Echidna aculeata. 
(Fig. 10.) 
The labyrinth of the spiny ant-eater possesses the special interest which 
attaches to all the organs of the monotremes. Before going on to consider 
the relationships of the different parts, however, the measurements may be 
given. 
The organ measures 11 mm. in its greatest length from the outermost 
point on the posterior canal to the innermost point on the cochlea. The 
whole diameter of the half whorl of which the cochlea consists is 6 mm. and 
the diameter of the tube of the cochlea itself just before its junction with the 
vestibule is 1°75 mm. The vestzbule measures 3°5 mm. in its longest diameter 
and the major axis of the oval window 1 mm. in length. 
The swperior canal measures rather less than 45 mm. in internal, and 
6 mm. in external diameter. The height of the vertex of the canal above 
the vestibule is 3°5 mm. and the diameter of the canal itself at the vertex is 
0°75 mm. The posterior canal measures rather more than 2°5 mm. in internal, 
and 4 mm. in external diameter. The height of the vertex of the canal 
above the vestibule is 3 mm. and the diameter of the canal itself at the 
vertex is 0°75 mm. The horizontal canal measures 2°75 1m. in internal, and 
4 mm. in external diameter. The height of the vertex of the canal above 
