916 PROFESSOR W. C. M'INTOSH 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, T 7 ^- 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, ■§ 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 Lahrus, T 7 g inch 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 border 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. — The general form of the ear of the wolf-fish on hatching is shown on PL XX. 

 figs. 2 and 4, and on PL XXL 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 cartilaginous 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. 



