glands of its own. But other glands moisten the tongue, as it lies in the recess of the lower jaw.

The tongue is a tube, the axial cavity of which is occupied by a slender cartilage, the glosso-hyal or ento-glossal, supporting nearly the whole length of the organ in its state of rest. The soft parts of the tongue consist of (1) epithelium; (2) pigmentary and submucous tissue separated by loose interstitial connective tissue from a fibrous sheath, and (3) longitudinal muscles, besides nerves glands and vessels. There is also an inner fibrous sheath with a smooth free surface, which glides over the glosso-hyal cartilage. The club has peculiar muscles, well described by Zaglas. The existence of minute smooth intrinsic muscles within the substance of the worm is still disputed.

It is probable that four sets of muscles successively promote the extension of the tongue, namely, (1) certain of the hyoid muscles, (2) the longitudinal muscles, (3) the smooth muscular fibres of the worm, and (4) the muscles of the club. Other hyoid muscles retract it. To the same muscles, however, different uses have been assigned by different observers. It has even been conjectured that the extended condition should be regarded as the more passive state of the organ. Others consider the protrusion of the tongue as a sort of erection; but such vascular turgescence must here play quite a subordinate part. Nor can the mere elasticity of the sheath effect much. We cannot here discuss these diverse explanations. The whole subject demands fresh researches. As Milne-Edwards has well said, the mechanism of this movement has not yet been explained in a satisfactory manner.

Though very carefully aimed, the tongue darts from the mouth as if its previous training thoroughly suited its own spontaneous energy. Perrault erroneously supposed that it was coughed out by air driven into it from the lungs. Bibron has graphically compared its expulsion to the act of spitting. Pagenstecher, on one occasion, saw a Chamæleon eject its tongue with such force that the animal lost its hold in consequence, and tumbled off the tree on which it was resting.

From the tongue of the Chameleon we naturally pass to its eyes. For by these the prey is first perceived, and if we could trace the intermediate changes which take place in the nervous system we should then be in a position to understand how the tongue receives the orders to do its work.

The eyes are relatively large. Each as a whole is nearly spherical, the equatorial slightly exceeding the axial diameter (8 8 millimeters). But what may be termed the morphological equator of the eye, corresponding to the border of the

sclerotic in front of the retina where the corpus ciliare and ciliary muscle are placed, is of no great extent. It gently rounds off into the region behind it, in a manner not conspicuous externally. The anterior portion of the eye is more strongly prominent.

The basal moiety of the sclerotic is exceptionally small. It is constituted by a round cartilaginous disc overlain by a layer prolonged from the much larger fibrous portion. This disc does not reach the optic nerve. The anterior zone of the fibrous moiety, surrounding the lens, is strengthened by a ring of peculiarly curved thin bony plates which are sunk in its substance.

The choroid is very thin, but is notably thickened posteriorly throughout the region subtending the yellow spot. A somewhat conical projecting pecten, about a millimeter in depth, covers the place of entrance of the optic nerve. The corpus ciliare is broader than the iris and pupil taken together. The muscles of the iris are extensive, as in birds; from the marginal sphincter fibres stretch backward towards the ciliary border, and behind these is a less powerful radial dilatator. The iris of the dead Chamæleon is half as wide as the pupil. It lies in complete contact with the lens. Its brilliant anterior surface has a dark background. Insignificant prominences replace the ciliary processes, anterior to which occur exceedingly weak meridional flutings. On the outer side of the corpus ciliare the ciliary muscle (tensor chorioidea of Brücke) arises from a conspicuous lamina of connective tissue, which reflects light and serves to support the cornea. The relative diameter of the cornea is less than in any other vertebrates except the turtles. The anterior chamber of the eye, containing the aqueous humour, is remarkable for its slight depth.

The lens, on the other hand, is strongly convex.

But of all parts of the eye the retina is most worthy of study, because of its large yellow spot. This, the region of exact vision, occupies the hinder pole of the retinal concave, and displays a central pit surrounded by a far extending zone, throughout which the retina is much thicker and beautifully modified in its minute structure. Especially modified is the so-called percipient layer.

The corresponding region of the human eye shows this layer to be furnished in the fovea proper with cones only. The yellow spot around it has many cones and but few rods, while in the remainder of the retina the rods greatly outnumber the isolated cones. Of two equal retinal areas that which has more numerous (and therefore more slender) cones permits more precise visual discrimination. Heinrich Müller dwells on the

following points of difference between the percipient layer of the Chamæleon and that of man.

1. The Chamæleon has no rods, but cones only.

2. The foveal cones in the Chamæleon are remarkably thinner than in man.

3. The (absolute) length of the foveal cones in the Chamæleon, notwithstanding its smaller eyes, is more conspicuous than in man.

4. The difference in the diameter of the cones, both in the peripheral and central regions of the retina, is greater in the Chamæleon.

5 The region corresponding to the human yellow spot is more extensive in the Chamæleon.

On the whole, sums up H. Müller, if we compare the human eye with that of the Chamæleon, the reptile has altogether the advantage.

Outside the bulb of the eye, but within the large though shallow orbit, the optic nerve, which is here remarkably long, makes a complex loop. It bends downwards, outwards, and again upwards (or even inwards, in certain positions of the eye), previous to its insertion.

Retractor muscles of the eye appear to be absent.

There is a large Harderian gland at the anterior angle of the eye, although the nictitating membrane is rudimentary. The lachrymal gland is small.

The two eyelids of man are represented by one great circular curtain, drawn over nearly the whole periphery of the protruding bulbus and circumscribing a small central orifice. A bony plate lies in the lower moiety of this lid. Beneath the skin of the lid, which resembles that of the general surface, is spread an extensive orbicularis muscle.

The free surface of the conjunctiva, very distinct from the adjoining lid, is also of unusual extent, reaching as far back as the equator of the bulb. The extraordinary mobility of the Chamæleon's eyes, in which it far surpasses all other vertebrates, is much aided by this arrangement, to which the curious curvature of the long optic nerve also contributes.

Thus, whether we consider the eye itself or its appendages, we have to do with an apparatus which is without parallel in the animal kingdom.

The male of the common Chamæleon differs but slightly from the female. He is known by his occipital crest, which is longer and higher, and by the shorter fold occupying the region of the neck.

The female lays a heap of sphæroidal eggs, grayish-white in tint, with calcareous, very porous shells. Oviposition has been

observed only in captivity. No one seems to have witnessed the hatching of the eggs, or to have determined the period of incubation. Brehm found that many females, even the strongest and healthiest,' die before or soon after the breeding season is over. He gives an interesting extract from Vallisneri, who noticed that one of his captive Chamæleons was for some days restless on her perch. Thence she slowly descended, moved about for a while, and at length paused in a corner of the floor of her box, which was covered with hard earth. In this she made a hole with one of her forepaws. For two days she worked, digging a pit about ten centimetres wide and fifteen deep. In this pit she now laid more than thirty eggs, and then, as she retired, pushed back the earth with her hindfeet, treating the heap of eggs as cats do their dung. Finally, she covered the heap with straw, dried twigs, and withered leaves.

That the Chamæleon bears living young is often untruly said. It is well known that in many so-called viviparous reptiles the egg is detained in the oviduct and there developed. What is thus normal in these may possibly occur as a rare (or pathological) exception in the Chameleon. But full proof is wanting.

EXPLANATION OF PLATE III.

(All the figures are of the natural size.)

FIG. 1. Rhampholeon spectrum, Günther, from the Camaroon Mountains. Male.

FIG. 3. Chameleon gallus, Günther, from Madagascar. Male.

FIG. 4. Head of Male Chamæleon montium, Günther, from the Camaroon Mountains.

FIG. 5. The same. Female.

FIG. 6. Head of the Male Chameleon Owenii, from Fernando Po.

FIG. 7. The same. Female.

111

THE NEW CHEMISTRY, A DEVELOPMENT OF
THE OLD.

By M. M. PATTISON MUIR, M.A., F.R.S.E.

IN a paper published in this Review (January 1878), I

endeavoured shortly to summarize the more important differences between that system of chemistry which was founded on a so-called equivalent notation, and the modern, or atomic phase of the science.

The general conclusion to which that summary led was, that the old chemistry was empiric, whilst the new is scientific; but, as was there remarked, empiricism precedes science: science is the natural development of empirical statements, and is not to be regarded as entirely a new departure.

Believing, as I do, that the old and new chemistry are essentially opposed in their methods, I nevertheless am certain that the germs, at least, of many of our modern chemical theories are to be found in the statements, and even in the hypotheses, of the workers of half a century since: and in the present paper I propose to trace, in a little detail, what I believe to be a correct outline of the development of two of the more important theories of modern chemistry.*

The chemical views most in vogue before the strictly modern epoch, were founded more on considerations of the composition of compounds than on the actions of these compounds. Dumas introduced wider views by recalling the attention of chemists to the fact that in order to frame even a tolerably complete system of classification, an answer must be given to the question, 'What does this substance do?' no less than to the other question, 'Of what is this substance composed ?'

* In the paper referred to, I briefly sketched the history of the development of the older doctrine of 'Equivalents' into the modern hypothesis of 'Valency.'