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Show 1870.] IN THE GROWTH OF SALMON. 43 " The term arrest of development of the Smolt, Mr. Buckland thinks, is not a scientific term. Nature has ordained that the fish should not grow more than a certain size in fresh water; that is to say, there is a maximum of growth and size in the Smolt. The transmutation of the Smolt into a Salmon takes place in the sea. Here, for the first time, we find that wonderful provision (which Mr. Buckland lays great stress on), the storing of fat on the pyloric appendages. Smolts have no fat on the pyloric appendages; but Grilse have. Non-migratory Salmonidae have no pyloric fat; but Sea-trout possess it. " The reason why Smolts will never become Salmon in fresh water has some relation to this development into the superior from the inferior stage of organization. This stage is not necessary for life. Salmon will live a long time in fresh water in the inferior condition, yet never pass over the line of demarcation between the two stages, unless conditions for the perfection of the secondary form be present. This is shown in the fact that nature actually orders a new coat for the creature when it passes from the one condition of things to the other. " If the migratory instinct is impeded by human intervention, the dress assumed at such times disappears, and the fish (by a happy provision of Providence) continues to wear its Parr-coat, which, as the fish gets bigger, becomes increased in intensity. The ** Heppers' already spoken of exemplify this. "The arrest of development is a term, therefore, which can only strictly be applied to Salmon in the sea, inasmuch as the arrest is simply the first natural stage of the progressive series of growths. Such stages of Salmon-growth have a parallel in the changes of insect-form: thus egg =ovum, caterpillar =parr, chrysalis = Smolt, and the butterfly -= Salmon, may be said to be the analogous stages whereby insect and Salmon pass from the imperfect to the perfect condition." Among what I have classed as addenda comes, as undernoted, a Table of dimensions (B). In the first notice (P. Z. S. 1868, p. 253) I was only able to give in detail those of specimen No. 1; but No. 2 has died since, and thus permitted its linear measurements to be taken. I have placed alongside these five other specimens, four of which are nearly similar in length, and the other that of a full-grown fish. These are specimens described individually by Dr. Gunther in his Catalogue, and have been chosen by m e to illustrate the proportional sizes and relations of the parts of the body to each other in an immature Salmon, a Sewin, a quasi-hybrid, a S. nigripinnis, and a fully developed S. salar. As the fractions used in the Catalogue are chiefly given in fourths, eighths, and sixteenths of an inch, I have converted these into decimals, enabling comparison between my two specimens and them more readily to be drawn therefrom. Columns I. and II. relate to the Society's specimens, described in the previous paper. Column III. relates to a young male Salmon (Parr), from the |
