918 PROFESSOR W. C. M‘INTOSH AND MR E. E. PRINCE ON 
ginous support of the ear is thinner and more shapely. Membranous lamelle divide the 
ear into the three spaces; the external chamber is covered by cartilage, and the 
posterior follows in the same manner as before. The large otolith hes at the inner and 
inferior angle near the notochord. 
A month subsequently the most noteworthy alteration is an increase in the amount 
and brittleness of the hyaline coating on the cartilage, and the same may be said for the 
succeeding month (June), fracture of the supporting skeleton of the ear frequently taking 
place in sections. The cartilage has diminished as a whole, its cells have become finer, 
and the brittle hyaline layer has increased in bulk. One of the most brittle regions is the 
inferior wall of the cavity lying to the inner border of the hyomandibular articulation. 
Olfactory Organ.—The chief point examined in connection with this organ was the 
formation of the two nasal apertures. In the earlier stages the single nasal slit assumed 
a vertical position, and at the beginning of April was of large dimensions. About the 
6th of the latter month a slight promontory was noticed in the middle of each lip of the 
fissure, and in ten days the promontories had met so as to make an aperture on each side. 
Each aperture on the 1st May was surrounded by an elevated rim, and the bridge had 
now become broad. At first the nasal slits lie in a hollow between the eyes, but at the 
latter date the snout projects further forward. The usual irregularities were observed in 
a series of specimens, some having the single slit on 21st May and with a considerable 
yolk-sac, others with the apertures fully formed—as just described. 
In Pleuronectes flesus, 4°; inch in length, the olfactory lobes are somewhat distant from 
the terminal sac, and the olfactory nerves pursue a course, parallel to each other, between 
the posterior process of the rostral cartilage and the trabeculae. On the floor of the 
cranium the two nerves rest upon a loose connective meshwork, and further back they 
bend inward, to unite with the olfactory lobes at the point where the superior and inferior 
oblique muscles of the eye have their origin on the cornu trabecule. 
A promontory on each lip of the nasal aperture has been already described in the 
goby, 44 inch long, large loosely aggregated cells forming an outgrowth from the radially 
disposed cells of the olfactory epithelium (see p. 910). In the post-larval wrasse, 4% 
inch in length, the transverse septum is complete, and the anterior and posterior nares 
are now distinctly separated. 
Sensory Organs in the Snout.—Remarkable sensory organs occur on the snout of 
the embryonic haddock (Pl. XXI. fig. 7), and are developed on the maxillary 
and mandibular elements in the  post-larval gurnard. When the latter has 
reached the length of ,°, of an inch, sections of the maxillary bar show organs like the 
sensory cushions in the otocyst or the papilla: along the dorsal and lateral surfaces of the 
trunk. The maxilla in section has the form of a flattened plate of hard hyaline tissue 
placed obliquely. This oblique bar gives off an upper arch, which bends over to meet a 
short crest sent up from the ventral margin of the bar. A rude tube, very angular in 
transverse section, is thus formed, but its outer wall is completed only at intervals. In 
the tube are seated certain sacs, on one side of which a cushion of columnar epithelium 
