often seen a flat filament, already formed within the corpuscle. In Mammalia, including Man, this filament is frequently annular ; some- times the ring is di\dded at a certain part, and sometimes one ex- tremity overlaps the other. This is still more the case in Birds, Am- phibia, and Fishes, in which the filament is of such length as to con- stitute a coil. This filament is formed of the discs contained ^vithin the blood- corpuscle. In Mammals, the discs entering into its forma- tion are so few as to form a single ring ; and hence the biconcave form of the corpuscle in this class, and the frequent annular form of the filament it produces. In the other Vertebrata, the discs contain- ed within the blood-corpuscle are too numerous for a single ring ; and they consequently form a coil. At the outer part of this coil, the filament, already stated to be flat, often presents its edge ; whence there arises a greater thickness of the corpuscle, and an appearance of being cut off abruptly at this part ; while in the centre there is generally found the unappropriated portion of a nucleus ; and hence the central eminence, surrounded by a depression, in those corpuscles which, from the above-mentioned cause, have the edge thickened. The nucleus of the blood- corpuscle in some instances resembles a ball of twine ; being actually composed, at its outer part, of a coiled fila- ment. In such of the invertebrata as the author has examined, the blood- corpuscle is likewise seen passing into a coil.
The filament, thus formed within the blood-corpuscle, has a re- markable structure ; for it is not only flat, but deeply grooved on both surfaces, and consequently thinner in the middle than at the edges, which are rounded ; so that the filament, when seen edgewise, appears at first sight to consist of segments. The line separating the appa- rent segments from one another is, however, not directly transverse, but oblique.
Portions of the clot in blood sometimes consist of filaments having a structure identical with that of the filament formed within the blood-corpuscle. The ring formed in the blood-corpuscle of Man, and the coil formed in that of Birds and Reptiles, have been seen by the author unwinding themselves into the straight and often parallel filaments of the clot ; changes which may be also seen occurring in blood placed under the microscope before its coagulation ; and simi- lar coils may be perceived scattered over the field of view, the coils here also appearing to be altered blood-corpuscles, in the act of un- winding themselves ; filaments, having the same structure as the fore- going, are to be met with apparently in every tissue of the body. The author enumerates a great variety of organs in which he has ob- served the same kind of filaments.
Among vegetable structiu'es, he subjected to microscopic examina- tion the root, stem, leaf-stalk, and leaf, besides the several parts of the flower : and in no instance of phanerogamous plants, where a fibrous tissue exists, did he fail to find filaments of the same kind. On subsequently examining portions indiscriminately taken from ferns, mosses, fungi, lichens, and several of the marine algie, he met with an equally general distribution of the same kind of filaments. The flat filament seen by the author in all these structures, of both ani-
