DEVELOPMENT AND LIFE-HISTORIES OF TELEOSTEAN FISHES. 905 



ridges and one superior internal ridge. The operculum in the various post-larval forms 

 presents no noteworthy points, except in the wrasse, ^ inch in length, in which a dense 

 plate of hyaline tissue appears in the tegumentary flap. 



Vertebral Column. — The first of the permanent skeletal structures in connection with 

 the notochord in Anarrhichas, are a pair of cartilaginous bars, which spring from the 

 upper side of the perichordal sheath at the sides of the spinal cord. These are developed 

 in a streaked, cellular region (mesoblastic) very evident beneath the muscular masses of 

 the parts. Each bar springs by a broad base from the notochordal sheath, passing 

 upwards to form an investment round the spinal cord. Early in February, a more 

 regular arrangement of cells takes place at the base, which is triangular in transverse 

 section, and in the investment, passing upward laterally, a transverse disposition of cells 

 occurs, forming indeed a cartilaginous bar — the neural arch. The firmness of this buttress 

 on each side dorsally, is probably the reason why the unprotected median arch of the 

 notochord bends upward in the preparation ; and the precursory thickening at the sides 

 inferiorly produces the same result in the ventral arch. At this time there are no 

 distinct interspinous cartilages, though there are signs of them dorsally. These structures, 

 however, appear in March, and towards the end of that month the neural arches meet 

 superiorly over a small canal, which has for some time been visible in the region. 

 Posteriorly they also send up dorsal processes — the neural spines. Above the latter is the 

 interspinous cartilage ; but the two do not touch.*" In the beginning of April, a some- 

 what conical cartilaginous process appears at a corresponding region in the lower arch, 

 but proceeds only a short distance downward above the segmental duct, being larger, 

 indeed, in the posterior than in the anterior region of the body. It gradually lengthens 

 so as to pass downward and outward over the subnotochordal region in which the artery 

 and segmental ducts lie. By the end of April, or early in May, these processes are 

 strengthened by a coating of hyaline ossific matter, continuous with that which has 

 invaded the notochordal sheath (PL XXVI. fig. 3, ncs). Instead of collapsing or becoming 

 wrinkled in sections, the sheath forms a firm, nearly circular ring. This hyaline and struc- 

 tureless ossific matter, like that seen in the premaxillary and clavicular elements, surrounds 

 the conical process of cartilage, so that in several sections it forms an isosceles triangle, 

 with a long apical process. The two dorsal arches are similarly coated with this matter. 



In post-larval stages of other Teleosteans, considerable variation in the character of 

 the elements of the early vertebral arch exists. In Cyclopterus, for instance, the basal 

 stumps of the neural arch arise as cartilaginous processes, developed as in Anarrhichas 

 within the perichordal sheath, and resting upon the chorda! investment. In the young 

 cod, § of an inch in length, the neural arch, as in the wolf-fish, appears to spring as a 

 hyaline outgrowth from the tubular investment of the notochord, which is formed of the 

 same hard tissue. In Cottus scorpius, when only •§ inch long, the notochord exhibits this 



* These probably correspond with Balfour and Parker's "two bars intervertebral^ placed, — two osseous plates on 

 the outer side of these, and continuous with the lateral osseous bars of the neural arch. The former give rise to cartila- 

 ginous elements above the osseous bridge of the neural arch in the adult." 



VOL. XXXV. PART III. (NO. 19). 6 Z 



