. British and Irish Salmonidae. Salmon. Fig. 18. Head of young hwn trout, natural size. Fig. 19. Head of old male hrook trout, 1-21 the natural size. If the external conformation of the head is examined it is found very similar in the young trout, fig. 18, to what is seen in the salmon par (see p. 52, fig. 13) while in the old trout, fig, 19, there are many points of resemblance with the old salmon (fig. 14, p. 52) ; but should the skulls be referred to (see plate i) bones of the trout will be seen to be much stronger and denser than in the salmon, and this is especially remarkable in tho
. British and Irish Salmonidae. Salmon. Fig. 18. Head of young hwn trout, natural size. Fig. 19. Head of old male hrook trout, 1-21 the natural size. If the external conformation of the head is examined it is found very similar in the young trout, fig. 18, to what is seen in the salmon par (see p. 52, fig. 13) while in the old trout, fig, 19, there are many points of resemblance with the old salmon (fig. 14, p. 52) ; but should the skulls be referred to (see plate i) bones of the trout will be seen to be much stronger and denser than in the salmon, and this is especially remarkable in those of the jaws and snout. At first the posterior extremity of the upper jaw in the young trout extends to beneath the eye, but with increasing age it reaches to behind it, and for two reasons, first the eye with age does not augment in size so rapidly as the rest of the head, so becomes comparatively smaller in old fish, and secondly the jaw on the contrary grows proportionately with the rest of the skull: as a rule the jaws are stronger in fresh-water than anadromous trout. As regards the size of the eye, should two trout of the same length but different ages be examined, the one which is the younger will have the larger eyes. Respecting the form of the preopercle in adult salmonidse, much has been written, but, as already remarked (p. 17), what has been asserted to be specific differences are often simply such as have been induced by age, sex, or local. Fig. 20. Fig. 21. Fig. 22. circumstances. Pig. 22, is that of an adult salmon; fig. 21, of a female Lochleven trout, 19 in. long; and fig. 20, of a salmon-trout, S. trutia, also 19 in. long, and having 52 csecal appendages. Trout from other localities, of the same size, show but very little individual differences to what is seen in the above figures.* The forms of the opercles will be subsequently alluded to and figured. Respecting the size of the fins of trout, those in fresh-water forms are generally more developed than in m
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