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sometimes take pains to display their beautiful colours; and we cannot believe that they would act thus, unless the display was of use to them in their courtship.

When we treat of Birds, we shall see that they present in their secondary sexual characters the closest analogy with insects. Thus, many male birds are highly pugnacious, and some are furnished with special weapons for fighting with their rivals. They possess organs which are used during the breedingseason for producing vocal and instrumental music. They are frequently ornamented with combs, horns, wattles and plumes of the most diversified kinds, and are decorated with beautiful colours, all evidently for the sake of display. We shall find that, as with insects, both sexes in certain groups are equally beautiful, and are equally provided with ornaments which aro usually confined to the male sex. In other groups both sexes are equally plain-coloured and unornamented. Lastly, in some few anomalous cases, the females are more beautiful than the males. We shall often find, in the same group of birds, every gradation from no difference between the sexes, to an extreme difference. We shall see that female birds, like female insects, often possess more or less plain traces or rudiments of characters which properly belong to the males and are of use only to them. The analogy, indeed, in all these respects between birds and insects is curiously close. Whatever explanation applies to the one class probably applies to the other; and this explanation, as we shall hereafter attempt to shew in further detail, is sexual selection.

CHAPTER XII.

SECONDARY SEXUAL CHARACTERS OF FISHES, AMPHIBIANS,

AND REPTILES.

FISHES: Courtship and battles of the males-Larger size of the females -Males, bright colours and ornamental appendages; other strange characters-Colours and appendages acquired by the males during the breeding-season alone-Fishes with both sexes brilliantly coloured -Protective colours-The less conspicuous colours of the female cannot be accounted for on the principle of protection-Male fishes building nests, and taking charge of the ova and young. AMPHIBIANS: Differences in structure and colour between the sexes-Vocal organs. REPTILES: Che'onians-Crocodiles-Snakes, colours in some cases protective-Lizards, battles of-Ornamental appendages-Strange differences in structure between the sexes-Colours-Sexual differences almost as great as with birds.

We have now arrived at the great sub-kingdom of the Vertebrata and will commence with the lowest class, that of Fishes. The

males of Plagiostomous fishes (sharks, rays) and of Chinæroid fishes are provided with claspers which serve to retain the female, like the various structures possessed by many of the lower animals. Besides the claspers, the males of many rays have clusters of strong sharp spines on their heads, and several rows along "the upper outer surface of their pectoral fins." These are present in the males of some species, which have other parts of their bodies smooth. They are only temporarily developed during the breeding-season; and Dr. Günther suspects that they are brought into action as prehensile organs by the doubling inwards and downwards of the two sides of the body. It is a remarkable fact that the females and not the males of some species, as of Raia clavata, have their backs studded with large hook-formed spines.1

The males alone of the capelin (Mallotus vllosus, one of Salmonida), are provided with a ridge of closely-set, brush-like scales, by the aid of which two males, one on each side, hold the female, whilst she runs with great swiftness on the sandy beach, and there deposits her spawn.2 The widely distinct Monacanthus scopas presents a somewhat analogous structure. The male, as Dr. Günther informs me, has a cluster of stiff, straight spines, like those of a comb, on the sides of the tail; and these in a specimen six inches long were nearly one and a half inches in length; the female has in the same place a cluster of bristles, which may be compared with those of a tooth-brush. In another species, M. peronii, the male has a brush like that possessed by the female of the last species, whilst the sides of the tail in the female are smooth. In some other species of the same genus the tail can be perceived to be a little roughened in the male and perfectly smooth in the female; and lastly in others, both sexes have smooth sides.

The males of many fish fight for the possession of the females. Thus the male stickleback (Gasterosteus leiurus) has been described as "mad with delight," when the female comes out of her hiding-place and surveys the nest which he has made for her. "He darts round her in every direction, then to his accumulated "materials for the nest, then back again in an instant; and as "she does not advance he endeavours to push her with his snout, and then tries to pull her by the tail and side spine to the nest.""

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The males are said to be polygamists; they are extraordinarily bold and pugnacious, whilst "the females are quite pacific." Their battles are at times desperate; " for these puny com. "batants fasten tight on each other for several seconds, tumbling over and over again, until their strength appears completely "exhausted." With the rough-tailed stickleback (G. tráchurus) the males whilst fighting swim round and round each other, biting and endeavouring to pierce each other with their raised lateral spines. The same writer adds,5" the bite of these little "furies is very severe. They also use their lateral spines with "such fatal effect, that I have seen one during a battle absolutely rip his opponent quite open, so that he sank to the bottom and "died." When a fish is conquered, "his gallant bearing forsakes "him; his gay colours fade away; and he hides his disgrace "among his peaceable companions, but is for some time the "constant object of his conqueror's persecution."

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The male salmon is as pugnacious as the little stickleback; and so is the male trout, as I hear from Dr. Günther. Mr. Shaw saw a violent contest between two male salmon which lasted the whole day; and Mr. R. Buist, Superintendent of Fisheries, informs me that he has often watched from the bridge at Perth the males driving away their rivals, whilst the females were spawning. The males" are constantly fighting and tearing each "other on the spawning-beds, and many so injure each other as "to cause the death of numbers, many being seen swimming near "the banks of the river in a state of exhaustion, and apparently "in a dying state." Mr. Buist informs me, that in June 1868 the keeper of the Stormontfield breeding ponds visited the northern Tyne and found about 300 dead salmon, all of which with one exception were males; and he was convinced that they had lost their lives by fighting.

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The most curious point about the male salmon is that during the breeding-season, besides a slight change in colour, "lower jaw elongates, and a cartilaginous projection turns upwards from the point, which, when the jaws are closed, occupies a deep cavity between the intermaxillary bones of the upper jaw."T (Figs. 27 and 28.) In our salmon this change of structure lasts only during the breeding-season; but in the

Noel Humphreys, 'River Gardens,' 1857.

5 Loudon's 'Mag. of Nat. History,' vol. iii. 1830, p. 331.

The Field,' June 29th, 1867. For Mr. Shaw's statement, see Edinburgh Review,' 1843. Another

experienced observer (Scrope's 'Days of Salmon Fishing,' p. 60) remarks that like the stag, the male would, if he could, keep all other males away.

7 Yarrell, History of British Fishes,' vol. ii. 1836, p. 10.

Salmo lycaodon of N-W. America the change, as Mr. J. K. Lord believes, is permanent, and best marked in the older males which have previously ascended the rivers. In these old males the jaw becomes developed into an immense hook-like projection, and

Fig. 27. Head of male common salmon (Salmo salar) during the breeding-season.

[This drawing, as well as all the others in the present chapter, have been executed by the well-known artist, Mr. G. Ford, from specimens in the British Museum, under the kind superintendence of Dr. Günther.]

the teeth grow into regular fangs, often more than half an inch in length. With the European salmon, according to Mr. Lloyd,' the temporary hook-like structure serves to strengthen and

8 The Naturalist in Vancouver's Island,' vol. i. 1866, p. 54.

9 Scandinavian Adventures,' vol i. 1854, pp. 100, 104.

protect the jaws, when one male charges another with wonderful violence; but the greatly developed teeth of the male American salmon may be compared with the tusks of many male mammals, and they indicate an offensive rather than a protective purpose.

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The salmon is not the only fish in which the teeth differ in the two sexes; as this is the case with many rays. In the thornback (Raia clavata) the adult male has sharp, pointed teeth, directed backwards, whilst those of the female are broad and flat, and form a pavement; so that these teeth differ in the two sexes of the same species more than is usual in distinct genera of the same family. The teeth of the male become sharp only when he is adult whilst young they are broad and fiat

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