DEVELOPMENT AND LIFE-HISTORIES OF TELEOSTEAN FISHES. 891 



ventrally directed flaps on each side of the diminishing median embryonic fin-membrane. 

 In the central core above referred to, a simple bar of cartilage passes downward from a 

 point immediately below the peritoneum, at the anterior border of the liver, and ends, 

 near the tapering margin of the fin-bud, in a dense aggregation of small cells deeply 

 stained in the preparation. In a Gadoid, f inch in length, similar cartilaginous plates 

 appear, not, however, in bold projecting flaps of the integument, but in flattened hori- 

 zontal ridges ; this difference in position being due, no doubt, to the flatter and more 

 obtuse character of the ventral surface in the post-larval Gadoid. Posterior to the paired 

 cartilaginous plates, which have an upper and a lower muscular mass, an expansion of 

 the integument forms a membranous fin supported by four or more hyaline rays. The 

 fin-rays at this time consist of paired hyaline rods, semilunar in transverse section, each 

 pair enclosing a strand of dermal tissue. A still later stage is seen in the post-larval 

 goby, ^ inch long, in which the two basal skeletal rods of the developing ventral fins 

 approximate, and are united posteriorly, forming an angle, with the apex directed back- 

 ward. Thus early is the union of the ventral fins effected which results in the disk -like 

 structure characteristic of the adult. The liver lies immediately over the developing 

 ventral fins, which are slightly anterior to the position they subsequently occupy. 



Median Unpaired Fins. — In the larval wolf-fish the marginal fin-membrane 

 commences behind the head in a position similar to that in the salmon, and extends 

 all round to the anus, and again forward in front of it to the yolk-sac. Proportionally 

 it is much less developed than in the salmon, and while the changes in its outline in the 

 latter are complex, those in the wolf-fish are less so. Moreover, whereas the marginal 

 portion of the tail of the salmon does not increase much at the period of absorption of 

 the embryonic fin, the contrary is the case in the wolf-fish, whose caudal expansion 

 attains large dimensions as the fin of the body diminishes. Whether this is altogether 

 due to the increase of the marginal web of the tail, or absorption in the other parts, is 

 doubtful. Probably both causes are concerned. The embryonic fin-rays appear first in 

 the caudal region, and afterwards in the anterior region. As the larval fish increases in 

 size, the marginal fin remains stationary, its further apparent diminution being due 

 merely to the general increase in the bulk of the body. It, however, increases in 

 thickness, and spinous rays are developed during the second month. On completing the 

 larval phase, i.e., on the absorption of the yolk in the beginning of June, the number of 

 dorsal spines is seventy-one; the first pair are separate, and the second diverge at the 

 tip, while the last is single and small. The ventral spines are forty -four in number, and 

 the last likewise is single and small. 



In the salmon the marginal fin (PI. XXII. fig. 4) shows, on emergence, considerable 

 differentiation. Thus the first dorsal is well marked, though it has only the granular 

 structure characteristic of the rest of the fin. The adipose fin is indicated by the eminence 

 situated between the former and the caudal, which is somewhat lobate, and generally 

 shows a slight notch above the tip of the notochord, marking, apparently, the homologue 

 of the embryonic tail-fin. The anal is distinguished by an elevation posterior to the anus, 



