In the strangely compound symmetrical bo dies of Gonium a provision fur separation appears to be made in the detached portions of which each perfect animal is apparently com posed. Time body of Gordian !perforate con sists of sixteen minute transparent globes of unequal size, arranged in the same plane. This beautiful animalcule is propagated by a separation of its integrant splierules, the creature dividing into four portions precisely similar to each other, and composed individually of one of the central globules united to three of the smaller marginal ones ; and no sooner is the division accomplished than the component globes of each portion increasing in number, the new animalcules assume the dimensions and appearance of that of which they originally formed parts.
In the Gonium pulvinatum the fissiparous mode of generation gives origin to a still more numerous progeny. The young animalcule is a minute, flat, diaphanous and quadrangular membrane, which swims through the fluid in which it is found by movements sufficiently in dicative of its animal nature : as it enlarges, the surface is seen to become marked by two series of parallel lines which cross each other at right an gles and divide the creature into smaller squares, which ultimately separate and become distinct representations of the original animalcule.
Some of the Nematoid worms, as the Nais, are likewise said to propagate by spontaneous division.
Gemmiporous generation.—This mode of re production, like the fissiparous, is confined to the lowest tribes of animal existence, and the creatures which propagate in this manner are unprovided with any apparatus specially appro priated to generation. The young appear as gem ma; or buds, which at certain periods sprout from the homogeneous parenchyma which com poses the body of the parent, and these buds gra dually assuming the form of the original by a kind of vegetative growth, become in a short time capable of an independent existence. The gemmiparous type of the generative function is met with through a wider range of the animal kingdom than the last, existing under modified forms in many species of Polygastric Infusoria, and of Polyps, as well as in Sponges, the Cys tiform Entozoa, and probably in some Acale phre.
It is in the Cystoid Entozoa that we find it in its simplest form. In the Cysticercus and like wise in the Ccenurus, the transparent membra nous bag of which the animal consists is filled with a glairy fluid, in which occasionally young hydatids are seen floating about. These young
Cysticerei in the earliest period of their forma tion are seen to pullulate from the parietes of the parent sac, and gradually enlarging they ultimately separate from their connexions, be coming detached and perfect animals.
Many of the Polygastrica are multiplied by a similar process, of which the Volvos globator may serve as an illustration. This beautiful ani malcule is a minute diaphanous globe, which under the microscope is generally seen to con tain a variable number of smaller globules, which are the young : these, when first discoverable, are attached to the inner surface of the parent, but speedily detaching themselves they are found rolling loosely within the body of the larger animalcule, effecting their rotatory move ments by the agency of cilia of extreme minute ness, which under a good microscope are seen to cover their external surface. The contained globules having attained a sufficient maturity, the parent volvox bursts, and thus by its own destruction allows its progeny to escape from their imprisonment. The multiplication of these animalcules is effected with considerable rapidity, and it not unfrequently happens that even before the escape of the second generation the gemmules of a third may be observed within their bodies, which in like manner advancing through similar stages of development will ter minate by their birth the existence of their parent.* It would appear from the observations of Professor Grant, that in the sponges, notwith standing their different form, the process of re production is entirely similar. In these curious animals the gemmules are developed in the substance of that living parenchyma which coats their porous skeletons, and when mature are expelled through the fcecal orifices to com mence an independent existence. When sepa rated from the parent sponge, these gemmules, like those of the volvox, are ciliated over a great portion of their surface, and being thus endowed with a power of locomotion, are enabled to swim to a considerable distance in search of a situation adapted to their future growth, until having at length selected a permanent support, they become attached, and developing within themselves the spieular or horny skeleton pecu liar to their species, they gradually assume the porous texture and particular character of the sponge from which they were produced.