136 THE INVERTEBRATA 



ally settling down by its broader end, while the other end develops 

 a mouth and tentacles surrounding it. The endoderm delaminates to 

 form the enteron. From the base of this first formed polyp there is 



Fig. 114. Bougainvilleafructuosa, x about 12. From Allman. A, The fixed 

 hydroid form with numerous hydroid polyps and medusae in various stages 

 of development. B, The free-swimming sexual medusa which has broken 

 away from A. 



an outgrowth along the surface of attachment which is the beginning 

 of the hydrorhiza. From this the rest of the colony is developed. 

 In Bougainiillea (Fig. 114) the polyps belong to the gymno- 



