162 Papers from the Department of Marine Biology. 



the common A. aurita of the Atlantic may occasionally give rise to 

 Aurellia labiata as a mutation, and that the Pacific species arose in this 

 manner. 



We will now give a brief account of the characters of the Scypho- 

 medusae. 



STRUCTURE, PHYSIOLOGY, HABITS, AND DEVELOPMENT OF 



THE SCYPHOMEDUS^. 



The Scyphomedusse are the large jellyfishes, commonly called the 

 sea-blubbers, in which the body is umbrella-shaped, the mouth parts 

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

 swims by means of a periodic expansion and contraction of the margin 

 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 contains 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 placed within the niches at regular intervals around the margin ; 

 but small as they are they are of vital importance to the jellyfish, 

 constituting its principal nerve centers, and if we cut them off, the ani- 

 mal commonly becomes paralyzed and is no longer able to pulsate 

 spontaneously. Mayer believes that the crystals or concretions within 

 the sense-clubs consist largely of calcium 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, forming 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 we find that a stimulus which is constantly 

 present causes periodic contractions followed by periods of rest which 

 are perhaps due to fatigue. In the case of the scyphomedusa Cassi- 

 opea 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. R. Gary finds that if they be removed and 

 the medusa be wounded in any manner the first stages in regeneration 

 are slow, but if even a single sense-organ be present regeneration pro- 

 ceeds at once and with 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 strictly proportional to the area of tissue, yet we may still 



