Invertebrate Gallery of the Indian Museum. 35 



The Scyphomedusx^ or Acraspedote Medusa;^ besides 

 being very much larger, differ from the Hydromedusx, or 

 Craspedote Medusa, in the following essential points : — 



(i) The muscle at the circumference of the medusa- 

 bell never projects into the cavity of the bell to 

 form a ' velum.' 



(2) Instead of a velum we find the edge of the swim- 



ming-bell produced into variously complicated 

 lobes and filaments (marginal lobes) into which 

 prolongations of the gastric cavity extend. 



(3) The manubrium, or gastric peduncle or oral tube, 



of the medusa-bell is provided with an ecto- 

 dermal oesophagus or gullet, and the edge of the 

 mouth is generally prolonged into long oral 

 arms. 



In some Scyphomedusse (the Rhizostomse) these 

 oral arms become deeply grooved, and the 

 edges at last curl over and meet to convert 

 the groove into a tube which, however, remains 

 unclosed at certain spots known as ' suctorial 

 mouths." The tubes of the oral tentacles lead 

 into the gullet, while the true mouth becomes 

 closed. 

 (4) Where the ectodermal oesophagus joins the true 

 endodermal gastric cavity special gastral fila- 

 ments, or gastric tentacles, usually in tufts, 

 are developed. 



(5) Another important difference, which, however, 



does not hold good throughout, is that the Cras- 

 pedote Medusa; {Hydromedusae) very seldom 

 (only in one family) give rise to secondary 

 medusae asexually by budding, whereas repro- 

 duction by asexual budding is not uncommon 

 among the Scyphomedusx. This is well seen 

 in the sflass model of Lucernaria. 



o 



(6) The sense-organs at the edge of the umbrella are 



always covered. 



