77 



From time to time it shifts its position, detaching its 

 " foot " and moving along on its " head " by means of its 

 tentacles, the outermost cells of which extrude little pseudo- 

 podia. It is continually drawing in and lengthening out 

 again, waving and curving its tentacles. 



-It often has a replica bud, a small daughter-hydra at- 

 tached to its body. Sometimes a bulging (the testis) is 

 seen just below the tentacles ; or nearer the " foot " (the 

 ovary). 



Two infusorians are often found on its skin, namely, 

 Kerona, which is probably commensal, and Trichodina, 

 which is ectoparasitic. 



Endoderm Cells 



Muscular Process 

 of Ectoderm Cell 



Interstitial Cell 



Cnidoblast- 

 Ectodern (Myoe- - 

 pithelial) Cell 



Flagella 

 Pseudopodium 



Vacuole 

 Nucleus 

 Symbiotic 

 Organisms 

 Mesoeloea 



FIG. 18. Portion of a transverse section of body-wall of Hydra. 

 (Highly magnified.) 



Describe the various kinds of Cells in Hydra, and state the 

 Parts of the Body to which they belong. 



The endoderm layer which lines the ccelenteron is com- 

 posed of large cells and some of them are T-shaped. The 

 crosspiece is a thin contractile portion of the cytoplasm ; 

 the stem or main part ol the cell is large and pear-shaped, 

 and has a nucleus, a big vacuole, green symbiotic organisms 

 which give the Hydra its colour, and also either pseudopodia 



