JELLYFISHES AND HYDROIDS 39 
bles a delicate seaweed or plume, but is in reality an animal. Each 
branch gives rise to a number of little flower-like polyp-mouths 
surrounded by tentacles which capture prey. 
Jellyfishes develop within capsules at the angles of the stems. 
These jellyfishes are set free and swim about for a long time, 
finally growing to be about one-quarter of an inch in diameter. 
Then they cast out their eggs which develop into plume-like hy- 
droids which in turn give rise to jellyfishes. 
The Rainbow Jelly, (Mnemiopsis leidyi), is one of the comb- 
jellies or Ctenophore. It is exceedingly abundant along our coast 
during the summer, but is so transparent that it would escape 
observation were it not for the brilliant flashes of prismatic red 
and green that play over its eight rows of comb-like flappers. 
When full grown the creature is about four inches long, and 
the outline of the body is pear-shaped with broad wings on the 
sides. At the narrow end there is a sense organ consisting of a 
capsule filled with a ball-like mass of concretions. This sense 
organ enables the creature to maintain its proper position in the 
water. The central stomach gives rise to a complex system of 
ramifying tubes which extend through the wings and along under 
the eight rows of combs. This creature is so delicately formed that 
it can not be lifted from the water without serious injury, yet it 
readily captures small fish and crustacea upon which it feeds. At 
night it gives out a brilliant green phosphorescence when disturbed. 
One often finds a long, pink, worm-like parasite imbedded 
within the gelatinous substance of the Rainbow Jelly. This is not 
a worm, however, but is a sea anemone, Ydwardsia leidyt. 
