|THE CAUSE OF PULSATION|
DIRECTOR OF THE DEPARTMENT OF MARINE BIOLOGY OF THE CARNEGIE INSTITUTION OF WASHINGTON
THE following is an account of a research which was pursued at the Marine Laboratory of the Carnegie Institution at Tortugas, Florida.
An interesting jellyfish, Cassiopea xamachana, lives upon the muddy bottoms of the lagoons of coral islands in the Florida and West Indian regions. Here the stilted roots of dense green mangroves fringe many a lagoon whose half stagnant waters have never felt the surge of ocean waves. Looking down through the clear depths one sees the bottom almost carpeted with the Cassiopea medusæ. Over wide areas they lie with their disks nearly touching and their bell-rims languidly pulsating. At a glance one might mistake them for sea-weeds, deceived as one would be by their delicate blue-green and gray-blue color, and by the tree-like shape of the branching appendages which bear the mouths of the medusa, and which project upward and outward hiding the pulsating disk below them.
At regular intervals around the rim of the jellyfish we find about sixteen minute club-shaped organs, each set within a deep niche. The microscope serves to show us that each of these little clubs contains at its outer end a mass of crystals, and upon one side a simple cup-like eye. Even in medusæ six inches in diameter these sense-clubs are smaller than the heads of the smallest pins; mere specks barely discernible to the eye, yet if they be cut off we find that the medusa ceases to pulsate, while the cut-off portion of the rim still contracts rhythmically. It is thus evident that the stimulus which produces each and every pulsation arises in the sense-clubs.