. Elements of zoology, or, Natural history of animals / ed. by Reese. Zoology. 523 ZOOLOGY. or other a large proportion of the solid rocks of our terrestrial surface. And thus we see the exemplification of a principle which has frequently come under our notice—that in the econ- omy of Nature nothing is insignificant; and that the most gigantic effects may be produced by the multiplication even of the humblest among the living inhabitants of the globe. CLASS XXIII—PORIFERA. 945. Of all the beings usually known under the designation of Zoophytes, the Sponges and their allies, constituting t
. Elements of zoology, or, Natural history of animals / ed. by Reese. Zoology. 523 ZOOLOGY. or other a large proportion of the solid rocks of our terrestrial surface. And thus we see the exemplification of a principle which has frequently come under our notice—that in the econ- omy of Nature nothing is insignificant; and that the most gigantic effects may be produced by the multiplication even of the humblest among the living inhabitants of the globe. CLASS XXIII—PORIFERA. 945. Of all the beings usually known under the designation of Zoophytes, the Sponges and their allies, constituting the class Porifera, appear to have the best claim to the title, since they present so complete an admixture of the characters of plants and animals, that it is difficult to say to which division they properly belong. Like plants, they are fixed to one spot during the whole of their lives—subsequently, at least, to their first deve- lopment; they seem to possess no sensibility, for they can be torn or wounded in any way, without showing by their move- ments any indication of being affected by the injury, and they do not appear to have that power of executing voluntary motions, which must be regarded as the distinguishing characteristic of animals. On the other hand, they present a structure which is not analogous to any thing found in plants, but is similar to that of beings undoubtedly belonging to the animal kingdom; with these beings they are connected by intermediate forms, presenting a regular gradation of increasing complexity of structure and variety of function; and there are certain move- ments, both in the adult and in the undeveloped Sponges, which are more analogous to those seen in higher animals than to any observed in plants. On the whole, then, the evidence for the animal character of the Sponges seems to preponderate, and they will be accordingly considered here. Still there is no doubt that, if they are included in the animal kingdom at all, the lowest pla
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