DEVELOPMENT AND LIFE-HISTORIES OF TELEOSTEAN FISHES. 907 



the salmon, and it is clear that in all in these parts the ossification is external to the 

 cartilage, to which it forms a coating. The dorsal and neural arches present numerous 

 cartilage-cells inside the osseous investment, where they spring from the column, but a 

 transverse row of large cartilage-cells occurs beyond this, and the whole at the end of 

 May is enclosed by a dense hyaline ossific layer. This hyaline sheath can often be cut 

 without fracture, so that it contains certain plastic elements. 



At the latest stage examined (as shown in specimens that survived till nearly the end 

 of June), after maceration, the vertebral column is found to consist of rings of firm 

 hyaline osseous tissue of considerable thickness, with spaces between the serial vertebrae. 

 To the dorsal and ventral aspects are attached the neural and haemal arches, which meet 

 and give rise to the spine. At the junction of these arches is a groove marked with 

 transverse striae — an aspect probably due to the remains, still visible, of the cartilaginous 

 elements. A similar translucent region occurs at the base of each pillar of the arch, at 

 the vertebral ring, and probably arises from the centre, now wholly removed. A com- 

 parison of this with the vertebral column of the young cod, obtained in tidal creeks in 

 the beginning of June, will show how advanced the latter species is. The vertebrae of 

 the cod are ossified from end to end externally, even more so than is indicated in Grassi's 

 figure of the bleak (op. cit., pi. vii. fig. 8), so as to be separated only by a thin inter- 

 vertebral edge, and the notochord is reduced internally to a moniliform band. 



In the newly-hatched salmon, cartilaginous spines, neura- and hsemapophyses, occur 

 on each side of the notochord above and beneath. They are fixed to the sheath of the 

 notochord, penetrate one-third its depth, and are best marked anteriorly. About the 

 sixth week the vertebral column presents a moniliform appearance, the neura- and 

 haemapophyses being adherent, but not continuous. Under pressure a tough moniliform 

 cellular central portion escapes, — the remnant of the notochord. The column has now a 

 distinctly barred appearance from the development of the vertebrae, each vertebral bar, 

 moreover, bisects the nail-shaped head of the neura- and haemapophyses. These last 

 named elements are exactly opposite each other in the darker portions, and on reaching 

 the column the terminal process expands into a nail-like head, having on each side a 

 pointed tip, devoid of cartilage-cells. The processes retain nearly the same shape as 

 formerly described at a much earlier period. At the present stage, however, the cells are 

 smaller and more crowded, and their nuclei are more distinct. At the tips of the larger 

 ones, near the tail, the cells are smaller, and more flattened, as well as more densely 

 arranged. Grassi* enumerates in the salmon and others four layers from within out- 

 ward, — (1) cellular stratum of the notochord, (2) epithelial coat, (3) proper membrane of 

 cord, (4) fine elastic amorphous membrane, — which is developed from the surrounding 

 embryonic connective-tissue. 



Ribs. — Little can be said in the way of addition to information already existing as 

 to the development of the ribs. They form long bars of finely cellular cartilage, at the 

 stage of date — 20th June, when the ring of hyaline ossific matter surrounds the notochord, 



* Op. cit. 



