JELLY FISHES. 91 



Why the pulsation occurs is therefore a mystery. If 

 it be for the purpose of breathing, we can as yet find no 

 respiratory organs. If it be for propulsion, it seems 

 quite inadequate to its office ; circulation there is none 

 that can be detected, and so we are driven to the 

 acknowledgment of our ignorance. 



How the pulsation is effected is equally a mystery. It 

 is easy enough to say that "the disc is composed of 

 innumerable polyhedral hyaline cells capable of con- 

 tractile efforts." But that is no explanation. We want 

 to know how the disc is able to keep up these pulsations, 

 though possessing neither muscular nor nervous fibres, 

 and as yet no one has been able to discover the secret. 

 The fact is known to every child who visits the sea- 

 shore and uses his eyes, but the wisest man cannot 

 explain it. 



There is another function, besides that of movement, 

 which is possessed by many of these Jelly Fishes, namely, 

 the power of stinging. This property was noticed by 

 the ancient naturalists, who gave to the Jelly Fish the 

 names of Acalepha3, i.e. nettles, or Medusa?, because the 

 long trailing filaments were venomous as the snakes in 

 Medusa's hair. 



Evidently intended for the purpose of paralyzing prey, 

 the poison-threads of the Medusre are sufficiently veno- 

 mous to cause intense suffering even to man, and in some 

 cases endanger his life. It is not only the pain inflicted 

 which constitutes the danger, but the effect on the heart 

 and respiratory muscles. The heart seems to cease 



