THE 



POPULAR SCIENCE 



MONTHLY. 



DECEMBER, 1908 



THE CAUSE OF PULSATION 



By ALFRED GOLDSBOROUGH MAYER 



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, Cassiopca 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 medusae. 

 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 medusa? six inches in diameter these sense-clubs are 

 smaller than the heads of the smallest pins ; mere specks barely discern- 

 ible 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 rhyth- 

 mically. It is thus evident that the stimulus which produces each 

 :and every pulsation arises in the sense-clubs. 



