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Show 1870.] IN THE GROWTH OF SALMON. 45 ment being in the less depth of the operculum, and smaller size of the dorsal and anal fins. The Sewin, excepting in a smaller ventral fin, is almost intermediate between the three foregoing. The hybrid (?) varies in proportional dimensions little from the preceding; the head may be considered a trifle longer than in them, as also the distance betwixt the dorsal and caudal fins, betwixt the pectoral and ventral fins, and betwixt the ventral and anal. Considering that the specimen of S. nigripinnis is a shade larger fish, its admeasurements wonderfully harmonize with the five already mentioned. What, therefore, appears to be elicited is that, pari passu, the fishes No. 1 and No. 2, fully four and five years old respectively, are almost identical in the relative proportions of their bodies with what may be assumed much younger Parr, Sewin Smolt, hybrid Sewin, and the so-called 5". nigripinnis. Taking column VII. into consideration, and contrasting it with III., the relative growths of the several parts of the Salmon's body to each other (from the Parr to the adult condition) are proved to be unequal in ratio. The total lengthening of the body, in the instances cited, is = 7 times. The depth of the body increases X 8. The head elongates X7'6. The least depth of the tail has an increment = X 5*9. The distance from the end of the snout to the eye enlarges X 12*1 times, or in the male the anterior segment of the face is proportionally excessively developed, a fact not at variance with the proportion between adult male and female Salmon. The maxillary bone grows in length x8*7. The distance between the eye and the opercular angle increases nine times from the Parr to the adult stage as a Salmon. The operculum widens x5*7, and its depth becomes = x 7. Betwixt the occiput and the dorsal fin the intervening space lengthens by x8*7, and that betwixt the dorsal and caudal fin 7*2 times. The elongation basally of the dorsal fin is = x 6*2, and its height •= x 5*1. The pectoral fin lengthens x4*4; but the increase of distance between the roots of the pectoral and ventral fins is = X 7'7. The elongation of the ventral fin proceeds to X 5*3 times, whereas the distance between the root of the ventral and the origin of the anal fin becomes =• X 10*5. The anal fin grows 5*9 times as long, the longest caudal ray X 5*6. The above data are of course only approximate, as from the comparison of only two specimens it would be unfair to draw conclusive deductions ; but, taken for what they are worth, computation gives the following general results :- 1. The average measurements of the development of the body, head, occiput to dorsal fin, dorsal to caudal, and pectoral to ventral fins are as 7*44 to 1. The amount of divergence between the ventral and anal fins, 10*5 to 1, is much greater than the foregoing maximum and minimum, an anomaly possibly dependent on sex. 2. The ratio of increase of the maxillary and the eye to that of the operculum averages 8*85 to 1. 3. The average elongation of the fins is as 5*26 to 1. |