DEVELOPMENT AND LIFE-HISTORIES OF TELEOSTEAN FISHES. 917 



The properties of the fluid of the chambers are quite adequate for the development 

 of the otoliths toward the internal wall. It is sufficient to point to the growth of the 

 Nemertean stylets to prove how perfectly such organs can be produced in successive 

 generations of the species. 



On 20th February a considerable increase in the otocystic cartilage of the wolf-fish 

 had taken place. From before backward this is marked superiorly by an increase in the 

 cartilage behind and above the eye, and inferiorly by a thickening of the bar behind. 

 The great development of the cartilage of the basilar plate around the anterior end of the 

 notochord gives this inferior bar a more distinctly horizontal position, one of its chief 

 flexures being caused, indeed, by the carotid. 



On 16th March the cartilaginous mass anteriorly and superiorly has increased so much 

 that it presents a complete ring in section, and thus somewhat further back the cartila- 

 ginous boundary is complete externally, while internally it ends abruptly opposite the 

 lower border of the optic lobe. It then sinks downward and presents a large perforated 

 median prominence below the ganglionic mass of the fifth, by which the auditory 

 nerve passes into the cavity. The latter contains large ganglion-cells and hyaline 

 coagulable lymph. After this swelling the cartilage diminishes internally, and ends on 

 each side of a median mass of connective tissue below the infundibulum. Beneath its 

 termination is a space and then an artery and vein (carotid and jugular). The pointed end 

 of the notochord begins above this median band of connective tissue. By and by the car- 

 tilaginous floor, now somewhat thin, glides in towards the notochord, and almost coalesces 

 superiorly. At this part it forms a thin wall externally, and ends in a thickened region 

 about half-way up, and the latter increases from before backward over the posterior semi- 

 circular canal, until a complete ring is formed round it, only a slender bar connecting the 

 latter inferiorly with the somewhat thickened end at the notochord. The contrast also 

 between the massive inner wall of the canal and the thin outer wall is marked. Then 

 (proceeding backward) the ring is broken internally, and only a slender line externally 

 connects the thickened superior loop with the thin horizontal bar leading to the noto- 

 chord. The superior mass diminishes and disappears, and the outer part of the horizontal 

 bar becomes disconnected from the denser region at the side of the notochord, the poste- 

 rior boundary of the ear being formed by a thickened mass of cartilage joined to the arch 

 over the spinal cord, and again forming a ring, as in front, before terminating. 



A month later considerable change had occurred in the otocyst — the chief feature 

 being the diminution of the cartilage, which is now covered by a layer of hyaline ossific 

 tissue, running from the notochord over the floor, and along the thin layer of cartilage 

 externally, but the thickened mass to which the hyomandibular is joined does not show 

 it distinctly. As soon as the bar becomes nearly horizontal (sloping a little upward and 

 outward from the cord), this hyaline coat extends from the cord to the upper and outer 

 border of the ear. The three semicircular canals seem to be similar to those in the previous 

 stage, but the ganglionic aperture in the floor anteriorly is less distinct, and the ganglion 

 lies more completely in it. The head of the hyomandibular is rounded, and the cartila- 



