First lines of physiology, being an introduction to the science of life; written in popular language . lly produced, two more animals will be con-structed in the same manner; and we know not how farthe process might be carried before the Hfe of the hydrawould be destroyed. In fig. 4, you see a single speci-men which has been split repeatedly in this manner,until it has formed seven hydras attached to the originalbody, and having a cavity or stomach common tothem all. 63. Sometimes the hydra splits itself Fig. into halves, each ofwhich becomes an independent ani-mal. 64. If we c
First lines of physiology, being an introduction to the science of life; written in popular language . lly produced, two more animals will be con-structed in the same manner; and we know not how farthe process might be carried before the Hfe of the hydrawould be destroyed. In fig. 4, you see a single speci-men which has been split repeatedly in this manner,until it has formed seven hydras attached to the originalbody, and having a cavity or stomach common tothem all. 63. Sometimes the hydra splits itself Fig. into halves, each ofwhich becomes an independent ani-mal. 64. If we cut one of these simplecreatures into a number of pieces inany direction, each piece will be found,in many cases, to complete itself andform a perfect hydra; but even here there is a limit tothe powers of life. If the division be carried too far, orif the animal be crushed, the fragments die. We cannotpowder a hydra, like a piece of hme, and yet leaveevery particle a hydra; because every thing that haslife is organized, and if we destroy any essential part ofits organization, it must cease to 50 HYDRA FORMED OF CELLULAR TISSUE. 65. In attempting to discover the real organization ofthe hydra, we perceive little in its substance but a massof soft and flexible membranes formed into cells con-taining an animal juice, which simple fluid answers thepurpose of blood, and supports the frame. The cells areso small that we cannot distinguish them by means ofsight, but w^e infer that they exist, because the fluid doesnot run out, at once, when we cut the hydra open, andthen subject it to light pressure. This membrane appearsto be more firm in some places than in others, probablybecause it is thicker, and perhaps because the cells aresmaller in such situations. The external surface of theanimal, which we may call the skin, has more firmnessthan the internal parts, but with this exception, there isnothing to distinguish one portion of the body or armsfrom another, and it is, therefore
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