12O 



COLLEGE ZOOLOGY 



and of the stalks of the hydranths constitute the cvnosarc (Fig 

 73, A, 5), and are attached to the perisarc by minute projections 

 The ccenosarcal cavities of the hydrocaulus open into those of 



medusa of Obelia. i mouth- , i onotheca B, free-swimming 



the branches and thence into the hydranths, producing in this 

 way a common gastrovascular cavitv. 



A longitudinal section of a hydranth and its stalk (Fig. 73 A 

 3 7) shows the ccenosarc to consist of two layers of cells 



