918 PROFESSOR W. C. M'INTOSH AND MR E. E. PRINCE ON 



ginous support of the ear is thinner and more shapely. Membranous lamellae 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 lies 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 Jlesus, T % 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 trabecular. 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 trabecular. 



A promontory on each lip of the nasal aperture has been already described in the 

 goby, -^ 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, y 7 ^ 

 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 (PI. 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 papillae 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 



