2. Alcyonella. 4. Cristatella.
Lamarck has comprehended under this name the four genera, Zoantha, Pedicellaria, Coryna. and Hydra. The first of these belongs to the Ita diata. The second appears to be merely organs of the Echini on which it is always found. The other two genera are distinguished by being naked, soft, fleshy zoophytes, without any distinct axis. The tentacula in these genera are not furnished with vibratory cilia. They present an external gemmiparous mode of generation. The Hydra are all fresh water animals, and the Coryna are found only in the sea. Genera.
I. Coryna. 2. Hydra.
This order comprehends the minutest and sim plest animals of the whole class. From their small ness, and their body being generally free, they were classed among the Infusoria by former naturalists. Their body is naked, soft, transparent, and with out any distinct internal axis or skeleton. There are no tentaeula around the mouths of the polypi, but the margin of the oral disk is surrounded with vibratory cilia. Some of these animals are beau tifully ramified, and all the ramifications are com posed of the same gelatinous contractile substance as the polypi. They are called Ciliata by Lamarck, from the cilia supplying in them the place of the tentacula of the other orders. The genera of this order are 1. 'cubic°laria. 4. Furcularia. 7. Vaginicola.
2. Norticella. 5. Brachionus. 8. Trichocerca.
3. Urceolaria. 6. Folliculina. 9. Rattulus.
The class of Infusory animalcules, as now de fined by Lamarck, is limited to those microscopic, transparent, gelatinous, aquatic animals, of a sim ple structure atad form, which are destitute of an internal digestive sac or stomach, and are nourish ed by superficial absorption. They are found only in fluids. T'ley present no trace of an osseous, muscular, nervous, or vascular system, nor any dis tinct internal organs for respiration, secretion, or generation. They generate either by a simple di vision of their body, or exhibit a gemmiparous mode of generation. The minutest animalcules discoverable by the aid of the microscope appear only as transparent moving points, or extremely minute gelatinous globules, without any perceptible external or internal parts. Some present a colour ed and somewhat opaque point in their centre, others are distinctly observed to move by the vi bration of very minute cilia variously disposed on their surface. In many animalcules we perceive a distinct internal cavity, which contains, not food, but the young, in form of minute globular gem males, as in the Volvox and Enchelis. The body
of the parent sometimes bursts to allow the escape of the young, and these species thus perish, like most insects, after a first generation. Many In fusoria have distinct external appendices, generally in form of a single or of a bifurcated tail. Some present circles of vibratory cilia on the anterior extremity of the body which, when in motion, ap pear like rotating wheels. The simplest animal cules, as the monads, give origin to new in dividuals, by their bodies gradually dividing either transversely or longitudinally, a mode of generation which is termed fissiparous. This fissiparous mode of generation is compatible only with the simplest kind of internal organization, and accords with di rect observation in proving their almost homoge neous internal structure. Blumenbach, and many other naturalists, have been led by numerous ex periments to believe that some kinds of animal cules may originate from mere combinations of the elements of vegetable or animal matter in a fluid state, without the aid of a previously existing pa rent. They have no distinction of sex, nor organs of generation. The spermatic animalcules which abound in the seminal fluid of all classes of the higher animals, form a connecting link between this class and the simplest Entozoa. Animalcules abound in decayed infusions of vegetable or animal matter, in decayed vinegar, in the secreted fluids of animals in the living state,in all stagnant waters, and in the waters of lakes and rivers. They are the food of zoophytes. We have found them in incalculable myriads in the water of harbours, and along our coasts, and at many miles distance from land among the Western Islands, and they probably abound not only in the waters of tropical seas, but in every drop of the ocean. They possess great tenacity of life. They suffer exposure to very high and very low temperatures without perishing. They may be dried to hardness, and again resus citated by the application of moisture. According to the experiments of Baker, Needham, and others, they may be revived by moisture, after remaining many years in a dried and apparently lifeless state. They form by far the most numerous class of be ings with which we are acquainted, although, from the difficulty of examining their structure and economy, they have least engaged the atten tion of naturalists.