OBELIA. 



31 



layer, but the latter forms a solid strand of cells 

 down each tentacle. The nematocysts are extremely 



ME 



EN 



Fig. 14. Obelia. 



A, a small portion of the hydroid colony. B, a free medusa in vertical section. 

 BL, blastostyle. C, calyx. EC, ectoderm. EL, endoderm-lamella. 



EN, endoderm. GO, gonads. ME, medusa. M, mouth of manubrium. 

 NE, nematocysta on the tentacles. OT, otocyst. p, perisarc. ST, stomach. 

 T, tentacles. V, velum. (Partly after Shipley and McBride.) A., X 50. 



B, x 12. 



