Page:The American Cyclopædia (1879) Volume XV.djvu/294

 SPONGE tive germs within; they are said also to grow by division, or growth of detached portions of the parent body; they are believed to be nourished by minute alga drawn within their pores. Some live in shallow, others in very deep water; scarce and small in cold latitudes, Sponge attached to its rocky bed. they increase in size and number toward the tropics, being most abundant in the Austra- lian seas. According to Dr. Bowerbank, there are 24 genera on the shores of Great Britain. While spongia is the type of the corneous sponges, thethys (Ouv.) and Grantia (Flem.) are types of the silicious and calcareous sponges respectively. (See PROTOZOA.) For the latest researches on the sponges see the papers now in course of publication (1876) by Prof. A. Hyatt, in the " Memoirs of the Bos- ton Society of Natural History," with figures and bibliography. Haeckel (MonograpMe der Kalk9chwamme, 1872) regards the sponges and acalephs as having been evolved from a com- mon ancestor, which he calls protascw, de- scribed as a body cavity surrounded by two layers of cells; he compares the sponge to the embryos of higher animals, both verte- brate and invertebrate. In his view, the germ of all animals, and the adult of such forms as hydra, may be reduced to the simple form of the young of a calcareous sponge, which he calls gastrula ; this he considers the " truest and most significant embryonal form of the animal kingdom." The sponges of commerce are procured chiefly in the Mediterranean and the Bahama islands ; most of them are obtained SPONTANEOUS GENERATION by diving, to which persons are trained from childhood in the Greek islands ; the adhesion to the bottom is generally firm, and the growth slow. To bleach sponges, the finest and soft- est are selected, washed several times in water, and immersed in very dilute hydrochloric acid to dissolve out the calcareous matters ; having been again washed, they are placed in anoth- er bath of dilute hydrochloric acid to which 6 per cent, of hyposulphite of soda dissolved in a little warm water has been added ; the sponge is left in this bath 24 hours, or until it is as white as snow. Smyrna is the chief place for the export of fine sponges. The coarse sponges used for horses and carriages, &c., are ob- tained chiefly from the Bahamas; when taken from the water they have a sickish, disagree- able odor, which soon becomes disgusting, like that of decomposing animal matter ; they are first buried in dry sand, and when decomposi- tion has ceased are exposed in wire cages to the action of the tide for purification. Fossil sponges are found in the Trenton limestone, and, if scolithus be a mining sponge, even as low as the Potsdam sandstone, and probably were in existence long before the oldest Silu- rian epoch. BracMospongia, discovered by the Rev. Mr. Hovey in the Birdseye group of the lower Silurian, is characterized by arm- like processes radiating from a central cup. Eospongia of Billings has been found in the lowest Potsdam. SPONTANEOUS COMBUSTION. See COMBUS- TION, SPONTANEOUS. SPONTANEOUS GENERATION, the direct pro- duction of living beings from inanimate ma- terial, in contradistinction to the ordinary mode of generation, in which young animals or plants appear only as the progeny of other living organisms. The views held by physi- ologists on the question of spontaneous gen- eration have varied greatly at different times. In the earlier periods of scientific culture, the Grecian naturalists, as represented by Aris- totle, recognized among animals three differ- ent modes of generation : 1, viviparous genera- tion, as in man and the quadrupeds, where the young were known to be produced alive from the bodies of their parents ; 2, oviparous gen- eration, as in birds, reptiles, and fish, where the young were hatched from eggs produced by the female; 3, spontaneous generation, where no connection could be traced between the young animals and any previously existing parents, and where they were consequently thought to be formed by the spontaneous organization of earthy deposits or decaying organic mate- rial. Spontaneous generation was therefore regarded as one of the regular and natural methods for the production of living forms; but as a physiological doctrine it rested en- tirely upon negative grounds, and was due to the incomplete knowledge then possessed by naturalists as to the real origin of many ani- mal species. Maggots, for instance, were thought to be formed by spontaneous genera-