Termo; and as we ascend in the scale, we come to still larger globules, which are manifestly composed of numerous globules of the same appearance and size as the Monas. Naturalists have discriminated several species of these minute creatures, the distinction of the species being founded chiefly on slight diversities in the figure of the body; the whole may be classed together under the name of Monades.

The next tribe consists of a distinct complication. To the globule of the Monas is added an appendage in the shape of a tail. These curious beings were first discovered by Leuwenhoeck and Hartsoeker, the inventors of the microscope. They are found only in other animals, and only in one particular apparatus, namely, in the organs of reproduction; and of the fluids contained in these organs, they exist only in one, namely, in the spermatic; hence the animals themselves are termed Spermatic Animalcules. Since

the time of Leuwenhoeck and Hartsoeker, they have been observed with care by many naturalists; though some philosophers have doubted their existence, others have positively denied it, and not a few have ridiculed the very notion as an idle fancy. This scepticism has arisen from the neglect of the instrument by which alone the fact of their existence can be ascertained, and affords a striking illustration of the extent to which preconceived opinions will operate on the mind even of the sincere and zealous cultivators of science. Ever since the middle of the seventeenth century, the means of setting the mind completely at rest on this subject have been within the

reach of every man; he had merely to open his eyes and look; and yet even persons who have been accustomed to philosophical research, having taken up the opinion that there is something inherently incredible in the statement, instead of carefully observing nature have contented themselves with smiling at those who have availed themselves of all the means of information in-their power. Lately these animalcules have been most diligently_examined by Prevost and Dumas. These physiologists have described, figured, and measured, in all twentysix species. It is found that every male of every tribe of animals that has been examined, and that is capable of producing its like, possesses a distinct species. Their existence has been ascertained in all the mammalia, in birds, in reptiles, in fishes; the examination hss been extended to several species of the mollusca ; in these also they have been found; lower down they have not yet been discovered. Ledermuller, indeed, has stated that he has seen them in the silkworm; but, as this observation has not been repeated, it remains in doubt. It is probable, however, that many things relative to this subject which are at present uncertain, will soon be set at rest, and that we shall know with exactness how far down in the scale of being these animals extend. They have lately attracted, and are at present occupying the attention of some of the most distinguished continental naturalists and physiologists, on account of their great importance in the function of reproduction. Their researches have already put us in possession of several new and curious facts.

which will be found to be of great interest and importance.

In

have termed a tail and a neck are nothing but the body itself attenuated to a certain extent. But at the next step in the ascending scale, distinct appendages are added to the body. These consist of hairs or bristles, which form special external organs. the tribe above, instead of a cavity without an aperture, we find the cavity distinctly opening at one extremity, thus forming the first rudiment of an alimentary tube. Next, processes or lashes are placed around the external margin of this aperture, which are endowed with the power of motion, by which motion the fluid in which the animal swims, and which contains its aliment, is propelled into its rudimentary digestive canal. To a body thus formed is added another appendage in the shape of a tail; to this succeeds a being so organized that the aperture leading to this internal cavity is not always open, but becomes capable of alternate contraction and expansion, thus coming very near to the idea we generally form of a mouth. As we continue to trace upwards the progressive complication of structure in these simple beings, we next come to an animal which consists of a distinct membranous tube, included in what may properly be termed a body. This constitutes the first rudiment of a special digestive organ. This tube assumes various shapes in its different portions, each portion being appropriated, it is reasonable to conclude, to different functions. The animals termed Vorticellæ are constructed in this manner. To this conformation there are added, in the ascending scale, external organs, which appear to form special organs of motion in

Without attempting at present to trace the progessive complication of the organization of animalculæ from the most rudimentary to the most perfect, though this has been sketched with great ability by Dr. W. F. Edwards, the brother of the physiologist formerly mentioned; and though this outline has been filled up at considerable length by Dr. Southwood Smith in the lectures already adverted to, who also exhibited with the microscope, specimens of most of these minute and curious creatures, it may suffice to state that this complication is as gradual as can well be conceived. The most simple of all, as we have seen, is a minute globule of the same size and aspect as the elementary globules of the primitive tissues of the higher animals. Then this globule becomes larger, and forms a body which is evidently vesicular. Next, groups of similar vesicles are united to each other. Hitherto there is no appendage whatever, no external organ of any kind. In the step above, to a globule very similar to the preceding, there is added an appendage in the shape of a tail. Such are the Spermatic Animalculæ. Above these the body is no longer absolutely simple; it consists of a number of globules enveloped in a common membrane without an aperture; such is the Volvox. Then this complex vesicle changing its figure, tapers at its posterior extremity into a tail, as in the Circaria, or at its anterior extremity into a neck, as in the Proteus. Still, up to this point, there is no true distinction of parts in the body of the animal; for what we

the form of wheels; the animals in which this structure is found derive their name from this peculiarity, and are termed Rotiferæ. The still more perfect have other appendages, in the form of tentaculi, similar to the processes which in the snail are termed its horns; and lastly, the most perfect of the class are provided with an external shell which forms a covering for their body. Such is the progressive complication in the organization of these curious beings, so far as this organization has been ascertained. The preceding sketch, rapid as it is, is sufficient to enable us to comprehend the discoveries which have recently been made relative to the connexion between animal and vegetable life, the statement of which is necessary to complete the view which we have endeavored to exhibit of elementary

structure.

Leaves and slips of the stem and branches of plants, whether herbaceous or ligneous, exhibit to the naked eye a substance so perfectly similar in appearance to the tissue which constitutes the main bulk of the animal solid, that it has received the same name. A great portion of the solid substance of the plant, as well as of the animal, is composed of cellular tissue. This tissue in the plant, as well as in the animal, is disposed in parallel lines or fibres. Grew and Malpighi had long since stated that these fibres consist of an assemblage of vesicles. Tréviranus, Dutrochet, and other modern physiologists, have proved that this account of their structure is correct, and have shown that these vesicles, when in a natural state, are so closely impacted, that they have an angular ap

pearance, from the degree in which they are compressed, but that they are capable of being separated by maceration, and that they assume a spherical or an oval form. Dr. W. F. Edwards, with a view of ascertaining with exactness the phenomena which take place in the progress of its decomposition, placed the leaf of a horsechesnut in water, and allowed it to remain there till the separation of its component parts was effected. He was so fortunate as to observe the whole process. He saw that some of the vesicles were still closely connected, and therefore appeared compressed; the figure of these was hexagonal; he observed that others at the margin, in consequence of the maceration were less compressed; these assumed a rounded form, and he perceived that the latter ultimately became completely detached from the cluster. But the most important facts ascertained by this acute and eminently successful experimentalist, relate to the phenomena exhibited by these detached vesicles, phenomena for which he was fully prepared both by the statements of other experimentalists, and by his own previous observations.

In the beginning of the present century, Girod Chantrans published a work on Confervæ, a large class of plants belonging to the order Algae or flags, in which the parts of the fructification are so small, that they cannot be clearly distinguished without the aid of the microscope. Chantrans announced that, in minutely attending to these plants, he observed that they occasionally exhibit phenomena of a very peculiar and extraordinary nature. He states, that the small tubes of which the

confervæ consist, sometimes open by one extremity into the water, and that in this case the vesicles contained in the tubes, which vesicles are the seminal particles of the plant, may be seen to be in motion, and that their movements, similar to those of the Infusoria, have every appearance of being as spontaneous as theirs. The account he gave of these phenomena appeared so incredible, that his statements were not believed, and sank into very general neglect. Subsequently, Tréviranus, one of the most distinguished physiologists in Germany, examined the confervæ, and announced that they do really exhibit phenomena similar to those described by Girod Chantrans. A few years afterwards, Barry de St. Vincent, a French naturalist, who, from long and laborious observation, had acquired a most extensive knowledge of microscopical plants and animals, resumed the subject, and found, on examining different species of confervæ, that the descriptions given by former observers were perfectly correct. He states, that the species of confervæ which he examined, similar in their structure to that of confervæ in general, produce seminal vesicles, which, when separated from the tube that contained them, remain for some time motionless; that after a certain period they begin to change their figure; that at the same time they acquire the faculty of locomotion, and exhibit every appearance of animal life; that at length, fixing to some solid body, they again undergo changes the most surprising; that they now become once more perfectly motionless; that immediately they begin to vegetate, and continuing to grow, at

last, form a plant of the same species as that from which they originally sprung. In consequence of these successive appearances of vegetable and animal life, he formed a new division for these genera of confervæ, intermediate to plants and animals. recently, M. Gaillon, a botanist of Dieppe, has published observations which agree with the preceding accounts, so far that he also states that the small vesicles contained in the tubes of certain confervæ, when separated from them, acquire spontaneous motion. This author adds the further observation, that in some of the species, particularly in the Confervæ Comoides of Delwin, the vesicles may at times be seen to move within the tube.

Dr.

Notwithstanding these several confirmations of the principal facts first observed by Girod Chantrans, they were not credited. Edwards, who could not imagine that the observations of so many distinguished men were entirely erroneous, and who, on account of the apparent similarity of the motion of these vesicles to that of the lower tribes of the Infusoria, was anxious to judge of the facts for himself, procured with this view different species of the confervæ. He found, on examining their structure with the microscope, that they consist of minute tubes, with partitions at equal distances, the interspaces being filled with vesicles of a yellowish green color. To the naked eye these tubes appear to be green filaments, finer than the finest hair. When first observed, the figure of the vesicles contained within them was found to be cylindrical. They were seen to adhere to each other by their

green