. British and Irish Salmonidæ. opinion of Agassiz, trout inhabiting rapid rocky streams have then- fins always muchdeveloped (Richardson, Faun. Bor. Ainer. p. 169). This opinion is not founded on observationsin nature. Salmonoids inhabiting such streams are distinguished by short fins, the delicateextremities being worn o& by constant activity of the fish, whilst individuals inhabiting stillwaters show the fins proportionately longer. Hence mature specimens have the fins more roundedand shorter than the sterile ones, on account of their greater activity. (Giinther, Catal. 149.) J Widegre
. British and Irish Salmonidæ. opinion of Agassiz, trout inhabiting rapid rocky streams have then- fins always muchdeveloped (Richardson, Faun. Bor. Ainer. p. 169). This opinion is not founded on observationsin nature. Salmonoids inhabiting such streams are distinguished by short fins, the delicateextremities being worn o& by constant activity of the fish, whilst individuals inhabiting stillwaters show the fins proportionately longer. Hence mature specimens have the fins more roundedand shorter than the sterile ones, on account of their greater activity. (Giinther, Catal. 149.) J Widegren likewise believed that sexually mature individuals have the caudal fin less deeplycleft than immature ones of the same age and size. 14 SALMONIDiE OF BRITAIN. this is a very noteworthy fact, as in some instances in which there exists adiscrepancy in the accounts of two authors as to the shape of this fin, such maybe owing, not to an error in facts, but to a difference in the method in which theexamination was when the muscles of the tail are of great fts. ^^ ?^, Fis- G. Caudal fm of a sea trout, expanded half aud two-thirds. Locomotion is the main use to which the fins of fishes are put, but even inlocomotion other forces arc frequently or rather generally brought iuto i)lay toassist the fins, whether such is for the purpose of swimming, or for leajiing as inthe salmon while ascending rapidsassistance. The skeleton* or cndo-skolcton of Salmonoids,consists essentially of askull and a vertebral orspinal column (to whichare certain appendages)these forming a protectionto the cerebro-spinal ner-vous system and largeblood-vessels present inthe long axis of the vertebra?, of whichthe spinet is made up,consist of a varying num-ber of bones, the bodies ofeach of which are excavated
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