the land. Among the thirteen classes into which zoologists generally divide the animal kingdom,* there are six which are exclusively aquatic; namely, the three classes of the depart ment of Radiata, the Jellyfishes, Echinoderms, and Polypes, which, with the exception of some few fresh-water Polypes, are, moreover, all marine. In the department of Mollusks, we find two classes exclusively aquatic, the Cuttlefishes and Clams. Finally, there is the great class of Fishes among the Vertebrates, which is entirely composed of aquatic animals. Among the seven other classes there is none, with the exception of the Birds, which does not contain aquatic animals. Thus we have, among the Mammifers, the important order of Whales, which are all marine; among the Reptiles, the Tritons and many frog-like animals; among the Insects, a number of water insects. As to the Crustacea, or Crabs, they are almost exclusively aquatic, since they number but a few small land species; the Worms, also, are mostly aquatic, as are likewise the Snails. In the present state of our knowledge, it may be safely stated that two-thirds of the animal kingdom are aquatic. But as the marine animals are much less known than the terrestrial, it is to be expected that their proportion will be increased very much, especially if we include in our survey the extinct or fossil species, which are for the most part marine.

Whoever has looked down in a shallow, quiet sea, and has beheld the variety of creatures of all sorts-crabs, snails, worms, star-fishes, polypes-which live among the sea-weeds, may have some idea of the amount of life which is concealed in these submarine abodes. It has been observed by an eminent traveller, (Darwin,) that our most thickly inhabited forests appear almost as deserts, when we come to compare them with the corresponding regions of the Ocean. And yet those animals which we are able to follow in their abodes, as they jump, run, swim, spin round, creep, or balance themselves among the sea-weeds, are nothing in comparison to that host of smaller creatures, imperceptible to our eyes, the infuso

* Mammifers, Birds, Reptiles, Fishes, Crustacea or Crabs, Insects, Worms, Cephalopods or Cuttlefishes, Gastropods or Snails, Acephals or Clams, Medusæ or Jellyfishes, Echinoderms, (Sea Eggs and Five Fingers,) and Polypes.

The fact of an animal being aquatic or terrestrial is best ascertained by the element in which it is born. Birds do not lay their eggs in the water, and therefore may safely be considered as land animals, although some species live almost exclusively on the water.

ria and foraminifera, - the number of which is daily increased by means of microscopic investigation, and which are all, without exception, aquatic. A single tuft of a small alga, or a bunch of polypes, is thus transformed into a forest quite as thickly inhabited as the shoal with its sea-weeds is to our naked eye. Besides, these minute animals are not, like most of the higher ones, limited to the shores and shoals; they are found even at the greatest depths of the Ocean, where no other animals seem to thrive. Mud from a depth of six thousand feet, on the coast of the United States, has been found by Professor Bailey to contain several new species of infusoria, and according to Ehrenberg, not only every sea, but to a certain degree the different depths of the Ocean, each contains species peculiar to it and not to be found elsewhere.

The number of individuals in the marine species is not less remarkable. We have only to reflect a moment on the quantity of fishes of different kinds, mackerel, cod, haddock, eels, &c., and also the number of lobsters, crabs, and clams, which are annually caught on the coast of the United States. Yet, in spite of these periodical destructions, they are found every year equally numerous. The phosphorescence of the sea affords us another striking evidence of the innumerable amount of individuals in certain marine species. In order to have an idea of it, one must have seen in a fine summer night the sea sparkling like a furnace at every stroke of the paddlewheels, and have ascertained by direct examination that each sparkle is a little animal. Or one must have seen in the daytime the surface of the water teeming with those beautiful, little, transparent creatures of the class of Medusa, (Beroe, for example,) and remember that these animals constitute the only food of the largest whales. Lastly, we may call to mind those coral islands of the southern seas, those whole archipelagoes, constructed by little animals of the class of Polypes, some of which are almost microscopic.

The sea along the coast of the United States is not inferior to any other, either in number of species or of individuals. Concerning the species that live near the shores, we have only to refer to the catalogues and surveys published by the differ ent States, and as to those that are found in deep water, we may state, as an instance of their variety, that in an excursion. on board of one of the vessels of the United States navy, among the shoals of Nantucket, it was only necessary to cast the dredge in order to get a rich collection of sea animals, for

the most part new species, or such as had not been noticed before on this side of the Atlantic. Among the species thus obtained, there is one which deserves a particular attention, in as far as it may be cited as an instance of the great amount of animal life existing unnoticed in the depths of the sea. The species in question belongs to a genus known to naturalists under the name of Salpa. They are little animals of the size of a small bean, gelatinous and transparent like crystals, and, what constitutes their most striking peculiarity, they are attached to each other in double rows, so as to form long strings like necklaces of crystals, which are called colonies. These curious animals had never before been noticed on this coast. The first specimens were dredged in an isolated state in the Vineyard Sound. Some weeks later, during the month of September, the vessel being at anchor in the bay of Nantucket, the surface of the water, immediately after a heavy shower, was suddenly seen teeming with elongated bodies like long transparent worms. The pilot, having been asked what these strange bodies could be, answered that it was the spawn of the Bluefish (Temnudon Saltator, Cuv.,) that came thus to the surface after a warm rain, as he had noticed it many times. Natural as this explanation appeared in consequence of the great numbers of those fishes which at that season of the year came to spawn in the bay, it could not entirely satisfy the naturalist who happened to be on board. He wanted to examine more closely the supposed spawn, and secured several strings. What was his surprise on finding, that instead of fish eggs he had before his eyes perfect animals, which not only moved by successive contractions, but in consequence of their great transparency allowed him even to examine in the most distinct manner the circulation within the body. They were seen that day only during a few hours, and disappeared suddenly towards sunset. Some days later, they came again still more numerous, and could be seen at the depth of at least five feet. It was thought that there were, on a moderate computation, fifty strings in sight, and as there were at least thirty individuals in a string, it was calculated that the total amount of individuals was not less than 500,000,000,000 for a square mile, without counting the free individuals.*

*The Salpas are among those animals in which that singular mode of reproduction, known under the name of alternate generation, is to be observed the offspring never resembling the parents, but the grandparents. In the Salpas, the aggregated individuals produce isolated young quite different in shape, and these, in their turn, produce again the strings.

This fact, whilst affording us an instance of the prodigious quantity of animals that may live unnoticed in the depths of the sea, makes it at the same time conceivable that so many whales as are known to have existed previously along these coasts, could find there are an abundant supply of food, in the absence of other similar gelatinous animals, (Beroe and Pteropods,) upon which they feed in the more northern regions.

If we consider that each marine species is circumscribed in limits which it does not pass, or, in other words, that they are subject to laws of distribution and association, as precise if not more so than those that preside over the distribution of terrestrial species, we must allow that to the zoologist, as well as to the philosopher, the conditions of aquatic life, and the peculiarities of the Ocean-bed by which these conditions are modified, are not less important to know than those which refer to the dry land.

Another consideration still increases the interest in these investigations; namely, the fact that it is chiefly by the study of the marine animals, and of the manifold conditions of soil, temperature, depth, and climate in which they live, that we are enabled to judge of the conditions of the earth in earlier geological periods, in as far as we may compare the remains of fossil species, their association, and distribution through the strata of the earth, with the condition of the analogous species now living on our shores.

The Ocean has also a great importance in a botanical point of view; for, although it be true that the marine plants are less numerous and diversified than the land plants, (the dry land being the chief seat of vegetable life,) there are, nevertheless, whole groups which grow in water, as, for example, the Algae and the Fuci. As in the animal kindgom, we find also among plants that the aquatic species hold an inferior rank, and in the same manner as the lowest animals, the Polypes, are exclusively aquatic, so we find the lowest plants, the Algæ, only in the water. It is thus in the liquid element that the two kingdoms meet. There we find those seeds of Confervæ that spin round like Infusoria, and there again grow those animals which have all the appearances of a plant, a root, a stem, branches, and whose flowers are living animals. It is therefore by a comparative study of these oceanic forms that we can arrive at a true understanding of the relations that exist between the two kingdoms, and perhaps finally solve the important question which has so long puzzled naturalists; namely,

where the limit is between plants and animals, if there be any at all.

As to the inferiority of the marine and aquatic species, we ought further to observe that it is not merely a general rule, applicable to the great divisions, but that it can also be traced in the details. Not only are the marine animals and plants as a whole lower than the land animals and land plants; but moreover, if we direct our attention to those groups (classes or orders) which contain both land and marine species, we shall generally find that the latter are the lowest. Thus, among the Mammifers, the aquatic tribes, the Whales, are undoubtedly the lowest; among the Reptiles, the Tritons and Frog; among the Insects, the aquatic kinds hold evidently a very low rank; and there can be no doubt that among the Snails, the few species that live on land are superior to the multitude of marine tribes. Neither is it to be overlooked that among those animals which, in consequence of a metamorphosis, change their condition of existence and pass from one element into another, the progress is constantly from the aquatic element to the dry land. Thus the tadpole, which is exclusively aquatic, respiring by means of gills, becomes an air-breathing animal when transformed into a frog. The mosquitoes are at first small and dull worms living in water, and become afterwards the restless creatures that fill the air. But there is no instance known of an animal becoming aquatic in its perfect state, after having lived in its lower stage on dry land. The progress invariably points towards the dry land. This fact becomes still more important, if we remember that the first animals and plants which appeared on earth in the primary or paleozoic epoch were aquatic, and that it is not until a later epoch, (the epoch of the coal formation,) that we find, for the first time, land animals and land plants.

From whatever side we may consider the laws of the organic creation,—in its actual distribution over land and water, or in its distribution in time through the geological ages, or in the physiological evolutions of some of the animal species, — we are invariably brought back to the liquid element as the starting point of all progress. We may then say that the modern investigations merely go to confirm this great idea, which was vaguely anticipated by the ancient poets and philosophers, when they tell us that the Ocean is the origin of all things.