. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. Ports of Entry -785 2. Statoreceptors In lower free-swimming animals the sense organs of equilibrium are usually statoreceptors of some sort, depending for their action upon differ- ences in the pressure of a comparatively heavy secreted mass, the statolith, which is brought into contact with surrounding sensory receptor cells when- ever there is a change in the position of the body. Around the margin of a floating jellyfish at the base of the tentacles th
. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. Ports of Entry -785 2. Statoreceptors In lower free-swimming animals the sense organs of equilibrium are usually statoreceptors of some sort, depending for their action upon differ- ences in the pressure of a comparatively heavy secreted mass, the statolith, which is brought into contact with surrounding sensory receptor cells when- ever there is a change in the position of the body. Around the margin of a floating jellyfish at the base of the tentacles that hang like a fringe from the edge of the "bell," there may be arranged a row of statocysts, each consisting of a hollow cham- ber lined with sensitive cells and containing a pendulous "clapper," which is made heavy by the deposition of limy salts in its end (Fig. 685). Whenever these fragile medusae in the course of their aimless voyagings upon the . . . Fig. 685. Statocyst of a me- surface of the ocean are tipped up at an un- dusa? Rhopaionema> consisting usual angle by the force of the waves or by of a weighted "clapper," sup- any other outside agency, the tiny loaded Plied with sensitive "hairs," , . , . ., . , within a sensory bell. (After clappers within the statocysts swing over and „ t. > ' v bump the sensory cells that are on one par- ticular side, with the result that the jellyfish rights itself sufficiently to bring the swinging clappers to a standstill, thus restoring equilibrium. If the statocysts half way around the margin of a jellyfish are carefully dissected off or destroyed in any way, the animal is no longer able to right itself, but floats about in an unnatural attitude in the water. Anyone who has ever heard the clang of a bell-buoy and seen it rock back and forth when the surrounding water is agitated can understand perfectly the way the statoreceptors of jellyfishes operate. Equilibratory mechanisms, presen
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