PHYLUM COELENTERATA 



147 



Stretch out to be slender threads five to seven centimeters in length. 

 They are very useful either singly or as a group in capturing and 

 delivering food to the mouth. The mouth is located in the center 

 of the distal end of the column and is surrounded by the tentacles. 

 This conical elevation between the bases of the tentacles in which 

 the mouth is located is called the hypostome. The mouth when 

 closed and viewed from the top looks something like an asterisk. 



Mouth 



Tentacle 

 Hypostome 



Battery of 

 Nematocysts 



Bud 



Basal Disc 



Fig. 69. — Hydra showing external features. 



From the side it appears simply as an indentation or notch in the 

 conical end of the hypostome. The proximal or attached end termi- 

 nates in a 'basal disc or foot, which secretes an adhesive substance 

 which helps the animal in attaching to objects. From one to several 

 luds are often found on the sides of the trunk, and these occasion- 

 ally bear buds before the first is separated from the original parent. 

 Buds are lateral outgrowths of the column and are found when the 

 animal has favorable living conditions. Budding usually occurs at 

 about the middle of the body in H. viridissima. Occasionally there 

 may be observed rounded projections on the side of the column which 



