this family; for the fissures on the margin of the shells of the genus Emarginula, of Pleurotoma, of Pleurotomaria, and of the holes formed by the notches in the edge of the lip of Haliotis, are filled up by layers of shelly matter of the same structure as the rest of the shell, and deposited in the same manner. These fissures, filled with this porous substance, may be seen on the inner surface of the valves forming lines of pores diverging from the tip, and increasing in width as they approach the edge, to the notches above referred to: they are useful in a zoological point of view, as showing the number of lobes into which the inner plate of insertion is divided.

The valves of the species whose shells are covered by the mantle bave a plain edge, with only one or two notches.

Those of which the shells are partly external have the inner coat of the valve produced beyond the outer coat, thus forming what is called the plate of insertion; for the valves of these animals do not simply cover the mantle as with a case, but have their edge inserted into the cartilaginous mantle, another character peculiar to this group. The inner plate of insertion, besides being divided into lobes by the fissures or slits above mentioned, has the edges of the lobes divided into deep grooves or pectinations.

The edge of the outer coat, which is never slit or lobed, is similarly but not so strongly pectinately divided, where it is inserted into the mantle.

This kind of edge is probably produced by the perpendicular radiating laminæ of which the two coats are formed, the number of teeth appearing to agree with the number and thickness of the plates, the teeth and laminæ being thicker and more numerous on the outer than on the inner coat.

This kind of edge does not occur, as far as my observation extends, in any other mollusca, for it is very unlike the grooves on the edge of many bivalves which are formed by the processes on the surface of the mantle, and more resembles the plates between the tubes in the substance of the valves of some Barnacles (Balani), but has no real resemblance to them in structure.

The more prominent peculiarities of this family appear to be,—

1. That instead of having a single valve, as is the case with most Gasteropodes, they have a series of more or less perfect valves placed in front of the normal valve, the front one being the most imperfect, all imbricated the one over the other.

2. Besides this increase in the number of valves, the surface of the mantle is covered with numerous rudimentary valves assuming the form of scales or spines. 3. These spines are sometimes placed in tufts symmetrically dispersed on the sides of the body.

4. The valves of the more normal Chitons, which are partly exposed, are furnished with two additional coats, of the size of the exposed part, not found in the shells of any other mollusca, the intermediate coat being of a porous texture; and this coat fills up the symmetrical slits usually found in the innermost coat.

5. The valves of these shells, instead of being simply placed on the surface of the mantle and attached to the animal by muscles, are inserted by their edge into the substance of the cartilaginous mantle.

Hence we may conclude, that though it is impossible to adopt M. DE BLAINVILLE's views with regard to the systematic arrangement of Chitons, yet they offer many particulars not found in other mollusca; and that in the structure of the edge of the valves, where they are inserted into the mantle, and in the formation of the central cellular coat, which is doubtless formed by small processes of the mantle, like the tubes in the substance of the valves of the coronal Cirripedes, they offer an analogy to the shells of those Crustacea which has not before been observed.

X. An Investigation on the Chemical Nature of Wax.

By BENJAMIN COLLINS BRODIE, Esq.

Communicated by Sir BENJAMIN C.' BRODIE, Bart., F.R.S., &c.

Received March 2,-Read March 30, 1848.

I. On Cerotic Acid, a new Acid contained in Bees'-Wax.

IN the summer of 1845, while studying at Giessen, in the laboratory of Professor von LIEBIG, I undertook, at the request of that distinguished chemist, the analysis of certain waxes which were the results of an experiment made by HERR GUNDLACH of Cassel, of feeding bees upon different kinds of sugar. It is not my intention to give those analyses here, and I mention them now only for the purpose of stating that it was this circumstance which first turned my attention to the inquiry of which I now offer the results to the Royal Society, and that it was in Professor von LIEBIG's laboratory that this investigation was begun.

Various chemists have before me undertaken a similar inquiry. The chemical history of a substance so abundant in nature and so useful to man as wax was always a curious question. Of late it has acquired a peculiar interest from our knowledge, derived from repeated experiments, that wax is formed in the organs of the bee, and that in the body of that insect that remarkable change of sugar into wax takes place, the knowledge of the true conditions of which would, we may hope, throw light upon the formation of fatty bodies, and on the way by which out of vegetable products the continual repair of the animal structure is effected. The first step to such a knowledge must be the accurate study of the chemical nature of those substances which are thus produced.

But little progress however has been made in this inquiry. I may sum up in a few words those results already known which, by my own experiments, I am able to confirm as true. It has been ascertained that wax is separable by alcohol into two portions, which have been called cerin and myricin; that, by the action of potash upon wax, an acid or acids may be obtained, and also an unsaponifiable body, cerain; and that by the distillation of wax we obtain volatile oils, solid hydrocarbon, and an acid which has been surmised to be margaric acid, from its resemblance to that substance.

I

say that these are the ascertained facts. The high atomic weight of these bodies, and the unavoidable errors of analysis, have rendered it easy to find formulæ for them, and to speculate as to their nature. If, however, the views which, in the fol

lowing pages, I offer to the Royal Society are correct, their true chemical relations and constitution have been undiscovered.

It would be useless, and it is by no means my intention, to comment upon all the ideas which other chemists have entertained upon this matter. There is however one theory, which has been advanced by certain chemists in France, of which it would be unbecoming in me to take no notice, both because it has a certain apparent amount of fact to support it, and because the originators of it, and others also, believe that they have finally settled the question of the true place which wax should hold in our classification of chemical substances*. M. LEWY has stated that cerin, that portion of the wax which is the more soluble in alcohol, is converted by oxidation by means of lime and potash into stearic acid. The method he pursued was that used by DUMAS with such success for the conversion of alcohol into acetic acid; of potatoe oil into valerianic acid; and for other similar transformations. He has explained the reaction by giving to the cerin the formula C68 H68 O4. On this hypothesis, the cerin, by conversion into stearic acid, loses three equivalents of hydrogen and takes up three equivalents of oxygen into its constitution, the reaction being expressed by the equation

C68 Hós O4+3HO=C63 H68 O,+H1=[ stearic acid ],

68

+H3

the cerin being considered the aldehyde of stearic acid. M. GERHARDT has taken up and extended this idea. Proceeding on the belief that the myricin and cerin are isomeric a belief, I may observe, not justified by experiment, although almost universally adopted by chemists- he has stated that the myricin, of which by far the larger portion of the wax consists, corresponds to the metaldehyde of the same acid, and in a paper which he entitles, "Faits pour servir à l'histoire de la cire des abeilles," has explained on this hypothesis the origin of the products of the dry distillation of that substance. The theory of M. LEWY agrees sufficiently well with his analyses of the substances in question and with the relations of his formulæ. I must however observe, that any person who will take the trouble of reckoning out those analyses on which the formula of stearic acid depends, according to the atomic weight of carbon now almost universally adopted by chemists, carbon 6, hydrogen 1, will see that this formula itself demands a new inquiry before we can accept it. These results of M. LEWY are in many ways at variance with my own experiments; but I confess that if the agreement of the analysis and of the meltingpoint of the substance he obtained by oxidation of the cerin with the analysis and the melting-point of stearic acid were in truth a sufficient proof of the identity of the bodies, this difference in our results would be to me very difficult to explain. Wax certainly stands in a remarkable relation to fat, but I do not believe that relation to be of the nature M. LEWY has conjectured, and I cannot but think that, in * Annales de Chimie, vol. xiii. p. 439; and Jahres-Bericht, BERZELIUS, vol. xxiv. p. 468. ↑ Ibid. vol. xv. p. 236.