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COLLEGE ZOOLOGY 



and of the stalks of the hydranths constitute the ccenosarc (Fig. 

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

 The ccenosarcal cavities of the hydrocaulus open into those of 



Fig. 73. — Hydeozoa. A, part of a colonial species, Obelia. 1, ectoderm; 

 2, entoderm; 3, mouth; 4, ccelenteron; 5, ccenosarc; 6, perisarc; 7, hydro- 

 theca; 8, blastostyle; 0, medusa-bud; 10, gonotheca. B, free-swimming 

 medusa of Obelia. 1, mouth; 2, tentacles; 3, reproductive organs; 4, radial 

 canals; 5, statocyst. C, larva (planula) of Laomedea. (A, from Parker and 

 Haswell; B, from Shipley and MacBride; C, from Parker, after Allman.) 



the branches and thence into the hydranths, producing in this 

 way a common gastrovascular cavity. 



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

 1 to f) shows the ccenosarc to consist of two layers of cells — 



