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 he 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 a hard 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- 

 oped upon these I'a- 

 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 



fig. 12; PASSION-FLOWER HYDROID (From Life). 

 Aniiis(iuam, Mass. 



