. Animal physiology. Physiology, Comparative; Physiology, Comparative. 110 STRUCTURE OF POLYPIFERA. to the influence of the surrounding water; but nothing like a heart, or a regular circulation, can be discovered. 131. We pass from these to a very remarkable group, which, though low in organisation, is second to none in regard to its importance in the economy of Nature,—the class of Polypifera, or coral-forming animals. This includes several tribes, which differ from one another in structure, to such a degree as almost to require to be distributed into three separate classes. The simple confor
. Animal physiology. Physiology, Comparative; Physiology, Comparative. 110 STRUCTURE OF POLYPIFERA. to the influence of the surrounding water; but nothing like a heart, or a regular circulation, can be discovered. 131. We pass from these to a very remarkable group, which, though low in organisation, is second to none in regard to its importance in the economy of Nature,—the class of Polypifera, or coral-forming animals. This includes several tribes, which differ from one another in structure, to such a degree as almost to require to be distributed into three separate classes. The simple conformation of the little Hydra, or fresh-water polype, has already been described (§. 14.); and this may betaken as the type of a number of compound structures, more or less re- sembling that of the Sertu- laria here delineated. Each of them consists of a stem and branches, of a horny texture; and on the sides or ends of these are a number of little cells or bell-shaped chambers, with their mouths upwards, in every one of which is a polype, bearing a strong resemblance to the Hydra. Each of these polypes is capable of living indepen- dently of the rest, obtains its nourishment by means of its own arms, and digests it in its own stomach; but all are connected by a set of vessels that pass along the stem and branches, in which a kind of circulation takes place, that strongly reminds us of that of the compound Tunicata (§. 126). This plant-like structure extends itself by budding; new branches are formed from those previously existing; these are enlarged at a certain. Fig. 72.— 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 Carpenter, William Benjamin, 1813-1885. London : Wm. S. Orr and Co.
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