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T H E
Vol. III.- NOVEMBER, 1869.–No. 9.
BY BRYCE M. WRIGHT, JR.
Do sponges belong to the animal or vegetable kingdom seems to be the first question which presents itself to our mind in investigating these curious organisms, and this question involves a definition of a boundary line between the two kingdoms, which, of all the most perplexing queries that can be found for an unlucky naturalist, perhaps is the most difficult. Eminent zoologists have, at various times, ranked them as belonging to the class of Zoophyta, but others equally clever have disputed this right, and have claimed them as belonging to the vegetable kingdom. In the celebrated work of Dr. Johnston on British Zoophyta, he disposes of them in a very summary manner. The following extract deserves attention : "if they are not the production of polypes, the zoologist who retains them in his province must contend that they are individually animals, an opinion to which I cannot assent seeing that they have no animal structure or individual organs, and exhibit no one function usually supposed to be characteristic of the animal kingdom. Like vegetables they are permanently fixed; like vegetables they are non-irresistible; their movements, like those of vegetables, are extrinsical and involuntary ;
Entered according to Act of Congress, in the year 1869, by the PEABODY ACADEMY OF SCIENCE, in the Clerk's Office of the District Court of the District of Massachusetts. AMER. NATURALIST, VOL. III. 57
their nutriment is elaborated in no appropriated digestive sac, and, like cryptogamous vegetables or algæ, they usually ramify and grow in forms determined by local circumstances, and if they present some peculiarities in the mode of the imbibition of their food, and in their secretions, yet even in these they evince a nearer affinity to plants than to any animal whatever.” This argument is certainly very favorable to their classification with plants, but there are other arguments by zoologists equally clever in favor of their classification with animals. Linnæus seems to have changed his opinion several times respecting them. In the commencement of his great work he considered them as plants, or at all events as very doubtful animals; but in a later edition of his "Systema Naturæ,” he seems to have admitted them along with the zoophytes in the animal kingdom.
In the opinion of Pallas, deBlainville, and others, they are intermediate organized bodies, without any determinate form, and with little susceptibility of feeling, but presenting an absorbent surface, and nourished pretty nearly like vegetables by the surrounding medium.
Sponges consist of a framework, or skeleton, coated with gelatinous matter, and forming a non-irritable mass, which is connected internally with canals of various sizes. The ova are very numerous, and present in appearance the form of irregular shaped granules derived from the gelatinous matter, which grow into ciliated germs and falling at maturity into the small canals, are then expelled by the orifices. When alive the body is covered by a gelatinous film, which, being provided with cilia causes a current of water to pass in at the smaller pores and out at the larger apertures, the sponge probably assimilating the nutritive particles which enter into the water. Papers have been written from time to time endeavoring to prove that the pores palpitate, but this has been stoutly denied, and perhaps the cause of their being moved in such a manner as to give rise to this discussion is in consequence of the action of the water in passing through them. According to the analysis of sponges by Hornemann, they consist of a substance "similar to osmazone, animal mucus, fat oil, a substance soluble in water, a substance only soluble in potash, and traces of chloride of sodium, iodine, sulphur, phosphate of lime (?), silica, alumina, and magnesia.” The quantity of silica which constitutes the structure of sponges is remarkable. It generally occurs in the form of spiculæ in considerable quantities, embedded in the substance or body of the sponge. In the species of Halichondria, the silicious spiculæ are pointed at the extremities, whilst the spiculæ of some are pointed at one end only, and are round at the other; sometimes they appear cylindrical, curved, or straight. The spicule of the genus Pachymatisma are often sharp at one extremity and at the other expand into two points; some are sharp at one end and expand at the other into three points; the P. Johnstonice can be taken as an example of the latter. Tethea possess silicious spiculæ having hooks at both ends, and amongst the genera Grantia, Geodia, and in the Levant Sponge, the spiculæ are very large and radiate into three directions like a three pointed star. When properly mounted they form very beautiful microscopic objects. The spiculæ of the Grantia nivea show them to be of the triradiate, or three pointed, star shape, those of the Halichondria Griffithic in the form of pins, whilst those of the common sponge, from the Philippine Islands, are sometimes in the shape of crutches or stars. In the common Madrepore Sponge (Dactylochalix pumicea) the silicious element is fully developed as the whole mass is composed of this extremely hard substance, which is disposed in tubular and radiating canals. One of the rarest, and I may say most beautiful of the silicious sponges, is the Euplectella* speciosa Gray (Fig. 76). It is described in the "Transactions of the Zoological Society
* The sponges are, by the most advanced zoologists, considered to be undoubtedly animals; all botanists reject them from the vegetable kingdom.- Editors.