Miscellaneous. 425 in form, structure, and functions, from the stem and branches, and could not, homologically, be compared with them. The nerves of the leaves did not all diverge at the same angle, neither did the branches. These last were exposed to various influences during the life of a tree, and in consequence diverged from the stem at various angles in the different periods of growth. It was therefore a dream of the imagination to hope to determine a typical angle of divergence, when the plant was endowed with a considerable range of variation to fit it for its place in the ceconomy of nature. Prof. Goodsir had listened to Dr. M'Cosh's paper with much interest, on two accounts : first, because it appeared to him that its author had, in endeavouring to reach one of the objects he had in view, embodied another attempt to investigate the laws of organic form by that precise or geometrical method, which can alone ultimately elevate natural history to the platform of the perfect sciences ; and secondly, because, although he could not admit all the conclusions at which its learned author had arrived, he yet believed the paper to involve a great truth. If he might be allowed to use the expression in reference to a plant, the specific physiognomy of a tree, as a mass, appeared to him to depend on the particular bulk, form, and grouping of its constituent masses. Now, if the form and grouping does not depend upon, it certainly involves, the mode of branching peculiar to the species. Dr. M'Cosh had restricted himself to the investigation of the law which regulated the latter ; but he had, and would meet with, that apparently at present insuperable difficulty in all such re-searches, viz. the variation within certain limits of the form of parts, or of the whole of an organized body, according to the particular con-ditions under which that part or that individual has been developed. Prof. Goodsir suggested that Dr. M'Cosh might be more successful if he would limit his inquiry to the law of ramification of a single judiciously-selected species ; and would endeavour to grow that species under such invariable conditions as might afford an approach at least to the typical form of the species. He also believed that before the law which regulates the arrangement of the primary and secondary ramifications of a leaf can be ascertained, attention must be directed to the law of form in the parenchyma itself. MISCELLANEOUS. On Parasitism. By M. Leon Dufour. Parasitism seems to be a law of nature, so generally does it prevail throughout the living world. This existence imposed in the creation upon other existences is at once a law of antagonism, of repression, and of guarantee for the maintenance of the harmony of nature. The attentive study of the articulated animals, and particularly of insects, presents to us the prodigies of parasitism in profusion, whether the lens examines the integument of the animals, or the science of the scalpel steps in to sound the depths of their organism. I have already had the honour to present to the Academy the
BioStor
