mals and plants, he states to be that usually denominated 2i fibre. Its appearance is precisely such as that of the filament formed within the corpuscle of the blood. It is known, he remarks, that discoid corpuscles circulate in plants ; and it remains to be seen whether or not filaments are formed also in these.
By gradually tracing the fibre or filament above-mentioned into similar objects of larger size, the author endeavours to show that it is not possible to draw a line of separation between the minutest fila- ment, and an object being to all appearance composed of two spirals running in opposite directions, and interlacing at certain regular in- tervals ; an arrangement which produces in the entire object a flat- tened form, and gives it a grooved appearance. It is, in fact, the structure which, for want of a better term, he has called d^. flat fila- ment. The edge of this filament presents what, at first sight, seem like segments, but which, in reality, are the consecutive curves of a spiral thread. A transverse section of such an object is rudely re- presented by the figure 8. This is also precisely the appearance pre- sented by the minutest filament, generally termed Fibre : and the author particularly refers to the oblique direction of the line sepa- rating the apparent segments in the smaller filament, in connexion with the oblique direction of the spaces between the curves of the spiral threads in the larger one.
The spiral form, which has heretofore seemed wanting, or nearly so, in animal tissues, is then shown to be as general in animals as in plants. Nervous tissue, muscle, minute blood-vessels, and the cry- stalline lens, afford instances in proof of this. And if the author's view of identity in structure between the larger and the smaller fila- ments be correct, it follows that spirals are much more general in plants themselves than has been hitherto supposed; spirals would thus appear, in fact, to be as universal as a fibrous structure.
The tendency to the spiral form manifests itself very early. Of this the most important instance is afforded by the corpuscle of the blood, as above described. The author has also obtained an interesting proof of it in cartilage from the ear of a rabbit ; where the nucleus, lying loose in its cell, resembled a ball of twine, being composed at its outer part of a coiled filament, which it was giving off to weave the cell-waU ; — this cell- wall being no other than the last-formed por- tion of what is termed the intercellular substance — the essential part of cartilage. These nuclei in cartilage, as well as those in other tis- sues, there is ground for believing to be descended, by fissiparous ge- neration, from the nuclei of blood-corpuscles.
The author then describes the mode of origin of the flat filament or fibre, and its reproduction in various animal and vegetable tissues, which he enumerates. He conceives that each filament is a com- pound body which enlarges, and, from analogy, may contain the ele- ments of future structures, formed by division and subdivision, to which no limits can be assigned.
He then traces the formation of muscle out of cells, which, ac- cording to his observations, are derived from corpuscles of the blood, to the state where there exists what is denominated the fibril. In
