Изображения страниц

calculation, and perception of external situation, are rendered possible by a highly developed nervous system, and the marvellously complex sensory organs combined with it, of which the eyes are especially remarkable. Independently of the generative organs, consisting of manifold parts of greater or less importance, the history of the multiplication and development of the bee demands a study of itself.

The function, and therewith the rank and value, of the bee's body seem to us higher than that of the polype in proportion as it is more complex. The superior complexity and variety of the parts is anatomically evident, and similarly the higher phase of the life. The superior energy of the existence, the functional capacity and perfection of the bee as contrasted with the feebleness of the polype, is obviously a result, or more correctly an expression, of the greater mechanical and physiological division of labour. In one animal, as in the other, life is spent in the function of self-preservation and the maintenance of the species, or reproduction; in both, the cycle of phenomena is limited, unbroken; but the means of execution are very different, and therefore the general effect is different. In the variety and correlation of the organs destined for the different manifestations of life, we have a standard for the rank of the animals. This rank has a twofold character, general and special. In other words, the position of an animal in the system is defined, first, by the general attributes, which it has in common with the forms harmonizing with it in the main characters of their organization; and, secondly, by the more special characteristics, which place the animal in its

own rank and station among its own immediate kindred.

Some insight into this classification of the animal kingdom is naturally indispensable to any one, who wishes to test and understand its reasons, and to render an account of it is an essential part of our task.

Since Cuvier's reconstruction of Zoology in the early part of this century, our science has been familiarized with the expression "type," or "fundamental form," introduced, long before, by Buffon. Cuvier, by extensive dissections and comparisons, first proved that animals were not, as people were formerly inclined to suppose, made on a last or shaped upon a block; but that they fall into several great divisions, in each of which expression is given to a peculiar constitution, arrangement, and distribution of the organs; in short, to a peculiar style. The sum of these characteristic. peculiarities, as well as the whole of the species united in it, was termed a "type." Various views, it is true, even now prevail as to the extent of several of these types or families, as we will already term them; but if we disregard the dubious, and in many ways suspicious, existences, generally comprised under the name of primordial animals, there is a general agreement as to the following number, but less as to the sequence of the animal types, than as to those groups, each of which has its peculiar physiognomy and special characteristic structure.

The class Colenterata includes the Polypes and Medusæ, and in the closest connection with it stands. the interesting class of the Spongiada, especially instructive as affording direct evidence of the doctrine of Descent. The organs of these animals are nearly always

arranged radially round an axis, passing through the dorsal and ventral pole. The cavity, which in most other animals-for instance, in man-is termed the abdominal cavity, the space between the intestinal wall and the abdominal parietes, is deficient in them; but, on the other hand, from the stomach proceed in general various kinds of tubes and branchia, which to a certain extent replace the abdominal cavity. Fig. 2 represents a

[graphic][merged small]

Medusa, Tiaropsis Diadema, after Agassiz. The darklyshaded organs form the so-called cœlenteric apparatus.

Of the Echinoderms, the reader is probably acquainted, at least with the star-fish (Asterias) and the sea-urchin (Echinus), of which the general form is likewise usually radiate. Besides a peculiar chalky deposit, or greater or less calcification of the skin covering, a system of water-canals forms a characteristic of this family. With these are connected the rows of suckers, which, by protrusion and retraction, serve as organs of locomotion. On account of the radiate structure prevailing among the Echinoderms, Medusa, and Polypes,

Cuvier believed them to be more nearly related, and introduced them altogether, under the name of Radiata. This similarity, however, is only superficial, for whilst, on the one hand, anatomy discloses the great difference of the Coelenterata and Echinodermata, the history of evolution still more decidedly banishes the Echinoderm from this position, and connects them more closely with the next division.

In this, that of the Vermes, the systematizer of the old school finds his real difficulty; in so many ways do they deviate from each other, so great is the distance between the lower and the higher forms; and after deducting the distinctive marks of orders, so little remains as a common character, so variegated is the host of smaller scattered groups, and even of single species, which demand admittance to the system of the Vermes. If we attempt to describe their typical nature in a few words, it must be something like this: The Vermes are more or less elongated, symmetric animals, which possess no actual legs, but effect their locomotion by means of a muscular system, closely combined with the integuments, which frequently become an actual muscular cylinder. To this we will add, that the perplexities and difficulties in reference to points of classification are transformed into sources of knowledge for the adherent of the doctrine of Descent.


The relations of the previous family with the type of the Articulata is so conspicuous, that the "kinship of the two was never questioned, even by the older zoologists. The very name of one, the highest division of the Vermes, that is, of the Annelids, or segmented worms, indicate this connection. This distinctive mark

of the Crustacea, Arachnida, Myriopoda, and Insecta, is that their bodies are constructed of sharply-defined rings or segments, the legs, antennæ and mandibles likewise sharing in this segmented character. A faithful expression of this segmentation is afforded by the nervous system, which lies, ladder-like on the ventral side, that is, beneath the intestinal canal, nearly encircling the gullet with its anterior loop. The display of segmentation is favoured by a deposit of horny substance, which gives a skeleton-like stiffness to the integuments.

The direct reverse is shown in the integuments of the Mollusca, our mussels, snails, and cuttle-fish. For although so many are supplied with protecting scales and shells, these are mere excretions from the actual skin, which remains soft, and characteristically moist and slimy, owing to the secretions of numerous glands contained in it, and has an inclination to lay itself in folds, and form a mantle-like investment to the body. The body therefore remains more or less clumsy; it possesses none of the grace of the Articulata, and especially of the insect; it is destitute of segmentation, and this deficiency is likewise evinced in the nervous system. This consists only of a ring, encircling the œsophagus, and a few smaller ganglia.

We shall most readily come to an understanding as to the Vertebrata, the family with which man is inseparably united. The essential part is the vertebral column, that portion of the internal and persistently bony or cartilaginous skeleton, in which the main portion of the nervous system is contained.

It is thus established that the systematic classification of the animal kingdom is based on certain prominent

« ПредыдущаяПродолжить »