58. First period.* — From the germination of the spore arises a tubular filament, which is converted directly, by successive divisions, into a simple riband-like frond, with a notch in its anterior margin, containing a young shoot. At whatever age the plant be ob served, the actively growing portions are shoots which resemble the spore plant in form and structure, and it is at various points of the upper surface of these shoots that the reproductive organs are developed.
59. The development of the antheridia com mences in the still very young shoot, by the separation "of a circular group of about sixteen of the superficial layer of cells from those of the tissue below it. There results a small lentil-shaped lacuna in the parenchyma, which divides by a vertical septum, parallel to a plane touching the centre of its outer sur face. This meets the perpendicular wall last formed at 450, and divides the cell into an external tetrahedral, and an internal three-sided compartment. The latter divides twice by septa, which cross each other at right angles, so as to form a central group, which, as it rapidly enlarges causes the four less actively growing cells b'y which it is sur rounded to assume a tabular form. In its further development it is converted into a rnass of very numerous and minute regularly arranged tessellar cells, in each of which is found " a lentil-shaped vesicle which occupies the greater part of its cavity." Shortly before the antheridium arrives at maturity, the mem brane of the cells disappears ; the vesicles float free, and there is now found rolled up in each, a spiral fibre of frora 21 to 3 coils, which is coloured yellow by iodine. The ripe antheridium presents the. general form and ap pearance shown in fig. 156. The cellular mem is filled with watery fluid, and roofed over by the cellular layer above mentioned." Each of the cells forming the floor of the lacuna, is divided by two septa, one parallel to the axis of the frond, and perpendicular to its surface, the other also perpendicular, but cutting the first at right angles. The membrane of each of the resulting small cells buds out upwards, so as to project into the lacuna, and soon after, the upper projecting portion is cut off from the rest by a transverse septum, and becomes the parent cell of the antheridium. A second septum is then formed above the first, and parallel to it. This is succeeded by a third, which is inclined to the horizon at a small angle. Above it is a fourth, similarly inclined, but in the opposite direction ; next follows a fifth, parallel to the third, and so on alter nately. In this manner is formed a cylindrical papilla, consisting of two vertical series of cells, each of which is a segment of a cylinder. Each
is next bisected by a radiating vertical septum, so that the papilla is now formed of four in stead of two vertical columns. The penul timate cell of one of these columns next brane, resulting from successive division of the four cells, which originally surrounded the central mass, gives way at the apex of the organ. In the meantime, the layer of cells which roofed over the lacuna has split open. The escaped spiral filaments (antherozoids), as seen under the microscope, soon after lose the vesicles in which they were enclosed ; " each slowly revolving round its own axis, lazily progresses in the surrounding water." 60. The development ofthe archegonia in An thoceros differs from that of all other Hepaticm in its rnuch greater simplicity. A single row of cells commencing at the upper surface of the young shoot, and directed towards its interior, becomes distinguished from those surrounding it by the quantity of granular mucus which it contains. The lowest cell of the series becomes larger than the rest. In its interior a daughter cell (germ-cell) which nearly occupies its cavity, is formed around a pre-existing central nucleus. The contiguous walls of the cells forming the remainder of the series are absorbed. Hence results a canal which leads from the surface to the cavity of the basal cell. It is difficult to believe that an arrangement so remarkable can have any other object than the admission of the anthe rozoids.
61. Second period.—Fruetification of the ar chegonia. In the greater number of archego nia, development ceases at the point above described. In those in which the germ-cell has received the influences necessary for its fructification, this last-named body enlarges rapidly, and very soon divides by a slightly embedded in the parenchyma of the stem of the parent, and causes absorption of its cells. The cells in the neighbourhood of the ori ginally six-sided canal leading to the germ, have in the meantime rapidly multiplied. The upper part of the canal now encloses the growing extremity of the rudiment, which, however, is separated from it by a quantity of fluid. It opens at the apex of a nipple-shaped projection of the upper surface of the frond, by a narrow aperture through which the coni cal upper extremity of the rudiment protrudes, and, as it rises, usually carries with it the remains of the cells immediately surrounding the narrow channel through which it has forced its way. It now presents the horn-like form, characteristic of the mature fruit, from which the generic name of Anthoceros is derived.