916 PROFESSOR W. C. M‘IINTOSH AND MR E. E. PRINCE ON 
side, and probably represents the commissure between the lobi posteriores, though these 
are not conspicuous. 
The median fissure of the medulla is at first dorsal and very large, but as the organ 
diminishes it assumes a lower as well as more central position, and becomes much 
smaller. 
Spinal Cord and Lateral Line.—In the extreme caudal region the posterior (dorsal) 
fissure of the cord, especially well seen in the wrasse, ;/; inch long, is reduced to a mere 
central canal, circular in transverse section, and surrounded by vesicular matter; indeed 
the white matter almost wholly ceases, and the column continues to its termination as a 
ganglionic tube, whose diameter is about one-quarter that of the notochord. This predo- 
minance of the grey matter in the hind part of the spinal cord is a character familiar in 
higher forms. 
About the level of the notochord in the cod, 2 inch in length, a canal internal to the 
corium passes along the outer edge of the septum, dividing the two median lateral 
muscular masses in the caudal trunk. It is of small diameter, though very distinctly 
marked on account of the presence of a sheath of black pigment, which continues into the 
intermuscular septa, and indicates the course of the delicate nervous strand connecting the 
canal, no doubt, with the spinal cord. Such connection cannot, however, be clearly made 
out, as the pigment passes only a short distance inward towards the cord. It is to be noted 
that the spinal cord has similar dark pigment in its protective tunic. The preparations 
do not show serial openings to the exterior at this stage, and the lumen of the canal is 
filled with loosely aggregated deeply-stained cells. In Labrus, 7; ich long, a canal 
cannot be made out in the caudal trunk; but an aggregation of cells occurs beneath the 
integument, on a level with the lower barder of the vertebral column. They lie below the 
pigment-layer of the skin, which stains deeply, and show evidence of nervous connection 
with the spinal cord. ‘The cells are large and folded, their walls being pushed in—in the 
form of a figure 8. No lumen in this instance can be discerned. 
Ear.—tThe general form of the ear of the wolf-fish on hatching is shown on Pl. XX. 
figs. 2 and 4, and on Pl. XXI. figs. 1 and 4. Cartilage develops much more rapidly in 
the salmon than in the wolf-fish in the otocystic region. Thus, in cutting the ear, 
both anteriorly and posteriorly, several sections show a complete investment of cartilage 
in the salmon; whereas at a similar stage in the wolf-fish the thin cartilaginous floor goes 
only a short distance upward externally, and at no part is a ring of cartilage completely 
formed. The inner margin of the cartilagimous floor of the ear bends downward 
posteriorly, and continues into the parachordals, which lie on each side of the notochord. 
Shortly behind this it also joins the hyomandibular cartilage, passing towards the middle 
line and disappearing. The general arrangement of the ear is similar in both species, 
though at no period does the inner border of the capsule pass so near the middle line in 
the wolf-fish as in the salmon. This is clearly seen in the neighbourhood of the noto- 
chord, The structure of the nervous cushions and their auditory cilia or stiff protoplasmic 
processes in the anterior and posterior chambers present no feature of note. 
