PRITCHARD'S NATURAL HISTORY OF ANIMALCULES.
LET the sluggard, who sits with his hands befbre him saying what shall I do, procure a microscope and Mr. PRITCHARD'S book. The wonders that a phial of water contains will excite his asto- nishment, anti perhaps rouse his faculties to active observation. He will find that all creation teems with life; that the fluids which seem to him a vacant medium are inhabited by myriads of living beings, too minute to be seen by the naked eye, yet-moving on in their respective walks of life, doubtless enjoying their brief existence, and continuing their races each after its kind. Their existence, however, is far from being the strangest matter : their organization is much more wonderful. In the compass of from 1-1200th to 1-24,000th part of an inch, digestive functions flou- rish; and in the larger species of Animalcules, if not in the smallest genus (Monads), the internal structure is as complex as in the higher animals. Hear Mr. PRITCHARD on the subject, and the mode of the discovery.
Until the introduction of vegetable colouring matter into the fluid, which sup- plies them with food—an experiment that has been attended with very success- ful results—these creatures were commonly supposed to be entirely devoid of in- ternal organization, and to be nourished by the simple process of. cuticular ab- sorption. By the application of coloured substances, which, moreover, have been found to invigorate rather than to depress the animalcule, and to maintain it in the full exercise of all its functions, this erroneous notion is set at rest, and an internal structure is discerned in some, equal, if not surpassing that of- many of the larger invertebrated animals, and comprising a muscular, nervous, and, in all probability, vascular system ; all wonderfully contrived for the perform. ance of their respective offices.
Their forms and modes of propagation are equally curious.
By a careful inspection of the drawings, it will be noticed that some animal.- cules resemble spheres, others are egg-shaped ; others, again, represent fruits of various kinds ; eels, serpents, and many of the invertebrated animals; funnels, tops, cylinders, pitchers, wheels, flasks, &c. ; all of which are found to possess their own particular habits, and to pursue a course of life best adapted to their peculiar constructions : thus, for instance, while some move through the water with the greatest imaginable rapidity, darting, leaping, or swimming, others merely creep or glide along; and many are altogether so passive that it requires. long and patient observation to discover any of their movements at all. One de- scription is perceptibly soft, and yields easily to the touch ; another is covered. with a delicate shell or horn-like coat. Of the latter order there are different degrees of density, as in the Volvox, Gonium, &c., where the envelope is corm. paratively thick ; and where, strange to say, the internal substance separates by the mode of propagation into several portions, forming so many distinct young ones, which at their birth burst the envelope, and tire parent becomes entirely dissipated. In others of this order, the shell is merely a plate covering the body, resembling that of the tortoise; sometimes it inclui:es the body, so as to leave only two small apertures at the extremities, ;mil at others it is bivalve, and encloses the creature like that of the oyster or muscle.
A reference to the plates, also, will convey a pretty accurate notion of the ex- traordinary methods of propagation with animalcules. All vetebrated animals are either oviparous or viviparous, which terms sufficiently designate their modes of production ; but it is not so with animalcules ; for in addition to these two methods-1. Animalcules propagate by a spontaneous seissure, or division of their bodies into two or more portions, each one forming a new creature, which, on its arrival at maturity, pursues the same course. These divisions take place in some genera symmetrically, as in the gonia, ; in others, by transverse, longitudinal, or diagonal sections. In these latter cases, the produce have forms differently proportioned from those of the creatures from which they spring ; for instance, figure 160 represents the young of 159, engendered by a transverse di- vision: this circumstance, we may observe, renders it sometimes difficult to de- termine the species. 2. They propagate, in the manlier before-mentioned of the volvox, and some other genera, by a distribution of the internal substance of the parent into a proportionate number of young ones, all of which at their birth issue forth, and leave behind them nothing but the envelope, soon to be dis- solved. 3. They are produced from germs, shooting forth from the parent's sides, as represented by fig. 218, &c. 4. From spawn, which, in the act of being shed, carries along with it a portion of the parent animalcule, as shown by fig. 80.
The study of Animalcules has one great advantage—the facility with which it may be pursued at any place and under any circum- stances. A good microscope, a simple instrument or two, with a little water, and the student is set up. He requires no expensive collections, no rare specimens to be gotten from distant countries, no large space to be occupied with paraphernalia of various sorts. A table holds his implements ; with a bit of vegetable substance for infusion in water, the creatures procure themselves. One ob- stacle alone appears to interpose itself to the general practice of this entertaining pursuit: a good and sufficient microscope, we opine, is dear—that is, about as dear as a loo-table or a good, baga- telle-board. To those, however, who are not deterred by the out- lay of a few pounds, we cannot conceive a more amusing piece of furniture for young people, or for children of a larger growth, when a wet day or listlessness renders them weary of themselves and wearisome to others. And to all who would study Animal- cules, we recommend their natural history by Mr. PRITCHARD. It is clear, popular, and scientific. He first presents us wills a brief yet sufficient view of the whole subject ; he then proceeds to the different genera, describing the respective species belonging to them. EHRENBERG'S arrangement of the Phytozoa forms the third book—dry and tabular ; but useful. An excellent table of contents, and upwards of three hundred engravings of magnified animalcules referred to in the text, complete the contents of the volume.
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