SCYPHOMEDUSAE COLLECTED BY STEAMER " ALBATROSS." 177 



occupying the position of the handle of the umbrella. The animal 

 swims by means of periodic expansions and contractions of the mar- 

 gin of the umbrella. If we look carefully, we will see that this 

 margin is notched at regular intervals, forming a series of lappets, 

 and that 8, or sometimes 16, of these notches are deeper than the 

 others and contain each a minute finger-shaped or club-shaped sense 

 organ which may be provided with an eye, but which always con- 

 tains a mass of crystals or concretions concentrated at its outer end. 

 These little sense organs are so small that they appear to the naked 

 eye as mere pigmented specks set within the niches at regular inter- 

 vals around the margin; but though small they are of vital impor- 

 tance to the jellyfish, constituting its principal nerve centers; and if 

 we cut them off, the animal commonly becomes paralyzed and is no 

 longer able to pulsate spontaneously. Mayer believes that the crys- 

 tals or concretions within the sense clubs consist largely of calcium 

 uric oxalate, and this makes it appear probable that sodium oxalate 

 is constantly forming in the sense club and that the calcium chloride 

 of the sea water, when it enters the sense clubs, is precipitated, form- 

 ing calcium oxalate, and in this manner setting free sodium chloride 

 (common salt), which is a powerful stimulant for the nerves, thus 

 causing the pulsating reaction. 



Thus in these animals it is found that a stimulus which is con- 

 stantly present causes periodic contractions followed by periods of 

 rest which are perhaps due to fatigue. In the case of the scypho- 

 medusa Cassiopea this stimulus is internal, for the sea water itself 

 neither stimulates nor inhibits the sense organs of the animal, the 

 stimulating effect of the interaction of its sodium, potassium, and 

 calcium being offset by the inhibiting effect of its magnesium upon 

 the motor centers. 



But the marginal sense organs do more than merely produce the 

 pulsation stimulus, for Dr. L. K. Cary finds that if they be removed 

 and the medusa be then wounded in any manner the first stages in 

 regeneration are delayed, but if even a single sense organ be present 

 regeneration proceeds at once and with normal rapidity. 



In general, if the area of tissue enervated by a sense organ be 

 large it pulsates more rapidly than if the area be small, and although 

 the ratio is not strictty proportional to the area of tissue, for accord- 

 ing to Dr. L. R. Cary (1917), the rate is reduced one-half when the 

 area is reduced to one-sixteenth. But young, small jellyfishes pul- 

 sate more rapidly than large, old ones ; yet if we graft two jellyfishes 

 together the small active one will force the large one to pulsate at 

 its own rate, which will be even more rapid than the normal rate of 

 the small one, due to the large area of tissue the sense organs now 

 control. 



101825°— Bull. 100—17 12 



