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 Secypho- 
meduse. 
STRUCTURE, PHYSIOLOGY, HABITS, AND DEVELOPMENT OF 
THE SCYPHOMEDUS-. 
The Scyphomedusz 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 calctum 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. Cary 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 
