Besides these doctrines of _Special Homology_ by which the bones of all vertebrates are referred to their corresponding bones in the human skeleton, and of _General Homology_, by which the bones are referred to the parts of vertebræ which they represent, Mr. Owen treats of _Serial Homology_, the recognition of the same elements throughout the series of segments of the same skeleton; as when we shew in what manner the arms correspond to the legs. And thus, he says, in the head also, the _basioccipital_, _basisphenoid_, _presphenoid_ and _vomer_ are {357} homotypes with the _centrums_ of all succeeding vertebræ. The _excoccipitals_,_ alisphenoids_, _orbitosphenoids_, and _prefrontals_, are homotypes with the _neurapophyses_ of all the succeeding vertebræ. The _paroccipitals_, _mactoids_ and _postfrontals_, with the _transverse processes_ of all the succeeding vertebræ: and so on. Perhaps these examples may exemplify sufficiently for the general reader both Mr. Owen's terminology, and the intimate manner in which it is connected with the widest generalizations to which anatomical philosophy has yet been led. The same doctrine, that the history of the Language of a Science is the history of the Science, appears also in the recent progress of Chemistry; but we shall be better able to illustrate our Aphorism in this case by putting forward previously one or two other Aphorisms bearing upon the history of that Science. APHORISM XXVI. _In the Terminology of Science it may be necessary to employ letters, numbers, and algebraical symbols._ 1. MINERALOGY. I HAVE already said, in Aphorism XV., that symbols have been found requisite as a part of the terminology of Mineralogy. The _names_ proposed by Haüy, borrowed from the crystalline laws, were so inadequate and unsystematic that they could not be retained. He himself proposed a _notation_ for crystalline forms, founded upon his principle of the derivation of such forms from a _primitive_ form, by _decrements_, on its _edges_ or its _angles_. To denote this derivation he took the first letters of the three syllables to mark the faces of the _PriMiTive_ form, _P_, _M_, _T_; the vowels _A_, _E_, _I_, _O_ to mark the angles; the consonants _B_, _C_, _D_, &c. to mark the edges; and numerical exponents, annexed in various positions to these letters, represented the law and manner of derivation. Thus when the primitive form was a cube, 1 _B_ represented the result of a derivation by a decrement of one row {358} on an edge; that is, a rhombic octahedron; and 1 _BP_ represented the combination of this octahedron with the primitive cube. In this way the pentagonal dodecahedron, produced by decrements of 2 to 1 on half the edges of the cube, was represented by ½ _B_² _C G_² ²_G_.