THE EYE OF FISHES.

265

On a closer examination, the lens is found to be composed of several thousands of regular transparent laminæ or spherical coats of uniform thick

ness: each of these la

minæ consists of about 2,500 fibres, extending from pole to pole of the sphere, and being consequently widest at the equator. The mode in which these fibres are fastened together, so as to resist separation and form a continuous spherical surface, is very curious; the contiguous fibres being united by

Direction of Fibres in Crystalline Lens of Cod

(magnified).

means of teeth, about 12,000 in each fibre, exactly like those of rackwork-the projecting teeth of one fibre entering into the

hollows between the teeth of

the adjacent one. As the fibres gradually diminish in size towards the centre of the lens and the teeth in the same proportion, so that the number of fibres or teeth in any spherical coat or lamina is the same from whatever part of the lens it is detached, it is not difficult to calculate their number. Thus the lens of a small cod, four-tenths of an inch in diameter, contains no less than five millions of fibres and sixtytwo thousand five hundred millions of teeth! A transparent lens exhibiting such a mechanism,' says Sir David Brewster, who was the first to investigate its wonders, may well excite our astonishment and admiration!'

As the eyes of the fishes are perpetually bathed by the water in which they live, we cannot wonder at the lachrymal apparatus

being totally wanting in their whole race; and as they are neither exposed to extreme variations of light, nor to the contact of dust, they generally also require no eyelid for their protection. In the common eel however, which bores cavities in the sand and mud at the bottom of the water, the eye is supplied with a hard and transparent membrane, which it can draw over the pupil at pleasure, thus effectually guarding these organs from injury. The eyeball of the herring is also defended by two vertical and transparent folds of the skin; and it is worthy of observation that where these folds decussate one another at their inferior extremities, the anterior one overlaps the posterior—so slight an impediment to progressive motion as the contrary position would have occasioned, having thus been foreseen and avoided.

As the external senses of fishes give them but few lively and distinct impressions, their pleasures are little varied; but, on the other hand, the painful impressions they receive from the external world are likewise circumscribed within narrower limits than those which bound the sensations of the birds and quadrupeds. Though often subject to the terrors of flight, they in their turn enjoy the excitement of pursuit; and a life of liberty makes them amends for the violent end to which they are generally doomed. Many a domestic animal or captive bird would willingly exchange its hard lot for the free life of the fish, who from the greater simplicity of his structure, his want of higher sensibilities, his excellent digestion, and the more equal temperature of the element in which he lives, remains free from many of the diseases which torment the higher animals.

The affections of fishes are cold as themselves; but, though the vast majority evince no sign of parental affection, and abandon their offspring to the mercy of the sea and their predatory companions, from the instant that the ova are shed, yet some at least show glimpses of that self-denying instinctive love for their young which often beams forth in so touching a manner among the birds or quadrupeds.

Thus, to preserve his eggs from the voracity of his brothers, the male stickleback collects the delicate fronds of water-plants or bits of grass that have been blown into the river, and forms them into a nest, the entrance of which he guards with the most sedulous care-repelling with tooth and prickles all other sticklebacks that approach the nest. If the enemy is too power

INSTINCTS OF NATURE.

267

ful, he has recourse to artifice-darts forth, seems actively engaged in the pursuit of an imaginary prey, and often succeeds in diverting the aggressor's attention from his nest.

The black goby, an inhabitant of the Mediterranean, likewise deposits its spawn in burrows dug among the roots of the seagrass, and, watching over the entrance of the house, opposes sharp rows of teeth to every intruder; and the hassar, which I have already had occasion to mention for his extraordinary land-excursions, is no less remarkable for his habit of constructing nests, which are quite as well-formed as those of the stickleback, and are made of grass blades, straws, and leaves. These nests are very plentiful in the little muddy streamlets that intersect the sugar-marshes of Guiana, so that the habits of the fish can be easily watched. The parent-fish is very jealous of the eggs, and waits near them until they are hatched, and the young family committed to the water. The parental solicitude of the hassar is shamefully misused by man for his destruction: a small basket is held before the entrance, then the nest is gently struck with a stick; and furious, with extended fins, whose sharp points are able to inflict a painful wound, the poor hassar darts into the fatal basket.

CHAPTER XXV.

REPTILES.

Defences of the Chelonians, Lizards, Frogs, and Toads-Locomotion of Serpents-Legs of the Tortoise and Turtles-The Gecko's Foot-The Chameleon-The Viper's Fang-How Serpents swallow their Food-Tongue of the Chameleon and of the Crocodile-Vertebral Teeth of the Deirodon-Maternal Affection of the Cayman Hybernation - Usefulness of Reptiles-Their Enemies and their Fecundity.

UNSOCIAL, indolent, obtuse, the friends of darkness and solitude, as if ashamed of exposing their hideousness to the broad light of day, the Reptiles seem to be fit objects both of abhorrence and pity; and yet their structure is as perfect and harmonious in its way as that of the most highly-gifted among the birds and quadrupeds, and all their wants have been as carefully provided for.

Who, on seeing a tortoise slowly creeping along, would not suppose that so slothful an animal must, necessarily, succumb to the attacks of enemies infinitely its superiors in swiftness, in cunning, or in strength? And yet it has, in most cases, but little to fear from their violence or speed, for its spine, ribs, and breastbone are wonderfully developed and soldered together, so as to enclose the whole animal in a solid panoply of bone. This harness, as trustworthy as any in which the knights of old encased their limbs when about to plunge into the tumult of battle, is covered by the skin, which in its turn is plated with large scales, while all the muscles and viscera are contained in the inner cavity. Only the head, feet, and tail protrude through openings between the dorsal shield or carapace and the ventral cuirass or plastrum, but can at the creature's will be withdrawn entirely under the former. Thus, at the approach of danger, the tortoise need only shrink under the cover of its im

ARMOUR OF THE TORTOISE.

269

penetrable bulwark to resist every attack by tooth or nail. The ventral part is less strongly plated, but most of the creature's enemies find it no easy task to turn it on its back, and thus to assail the fortress on its weakest side. As several species attain

a considerable weight, their mere bulk constitutes a good defence; and if it should be imagined that this protection could, after all, only avail for a short time, as in all probability the want of air must soon force the animal to stretch its head out of its hiding-place, yet this emergency has also been well provided for, as, having a cold blood, the tortoise can remain a long time without breathing-long enough, at least, to tire the patience of the most obstinate foe.

The turtles and river and marsh tortoises are not able, like their brethren of the dry land, to withdraw entirely under cover, but, as they are excellent swimmers, they stand less in need of this passive defence; besides, many of them are so strong and of so ferocious a disposition that, instead of fearing others, they are themselves objects of fear to most of the creatures that come within