36 SEA-SHORE LIFE 
finger of a glove. If the tentacles come in contact with a small 
fish or crustacean these little stinging-threads are instantly dis- 
charged, and on account of their minute size they penetrate the 
skin of the prey carrying with them a poison, believed to be formic 
acid, which quickly paralyzes the victim. Scattered between the 
tentacles there are numerous little balancing organs, which may 
also serve to detect 
vibrations in the 
water. These organs 
consist of minute 
capsules each con- 
taining ahard spher- 
ical concretion. The 
stomach of the me- 
dusa is a four-sided 
tube at the centre 
of the concavity of 
the bell. 
Four canals ra- 
diate outward from 
this stomach and ex- 
tend 90° apart, to a 
vessel which encir- 
cles the bell margin 
at the bases of the 

tentacles. The geni- 
tal organs are devel- 
Fig. 12; PASSION-FLOWER HYDROID (Fyrom Life). 
Annisquam, Mass. 
oped upon these ra- 
dial canals. They 
are ribbon-like, but each ribbon is longer than the portion of the 
canal upon which it is developed, and its edge is therefore folded 
sinuously from side to side. 
The stomach, genital organs and tentacles are rich brown in 
color with green spots, while the other parts of the jellyfish are 
transparent and gelatinous. 
According to Perkins, the jellyfish is very active upon cloudy 
days, when it swims rapidly upward to the surface, opening and 
closing its umbrella-like bell with powerful pulsations. Upon 
