. The ancient life-history of the earth; a comprehensive outline of the principles and leading facts of palaeontological science. Paleontology. Fig. 188.—Sipho7iiafiais. Upper Greensand, Europe. Fig. 189.— Ventriadites simplex. White Chalk, Britain. really composed of this substance, and are therefore genuine " Siliceous Sponges," like the existing Venus's Flower-Basket (Euplectella). Like the latter, the skeleton was doubtless ori- ginally composed, in the young state, of disconnected six- rayed spicules, which ultimately become fixed together to constitute a continuous frame-work.
. The ancient life-history of the earth; a comprehensive outline of the principles and leading facts of palaeontological science. Paleontology. Fig. 188.—Sipho7iiafiais. Upper Greensand, Europe. Fig. 189.— Ventriadites simplex. White Chalk, Britain. really composed of this substance, and are therefore genuine " Siliceous Sponges," like the existing Venus's Flower-Basket (Euplectella). Like the latter, the skeleton was doubtless ori- ginally composed, in the young state, of disconnected six- rayed spicules, which ultimately become fixed together to constitute a continuous frame-work. The sea-water, as in the recent forms, must have been admitted to the interior of the Sponge by numerous apertures on its exterior, subsequently escaping by a single large opening at its summit. Amongst the Cosknterates, the " Hydroid Zoophytes" are represented by a species of the encrusting genus Ilydractmia, the homy polypary of which is so commonly found at the present day adhering to the exterior of shells. The occurrence of this genus is of interest, because it is the first known instance in the entire geological series of the occurrence of an unques- tionable Hydroid of a modern type, though many of the exist- ing forms of these animals possess structures which are per-. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Nicholson, Henry Alleyne, 1844-1899. New York, A. L. Fowle
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Keywords: ., bookcentur, bookdecade1870, booksubjectpaleontology, bookyear1876
