Chap, iv.] INTRACELLULAR DIGESTION. 



I0 5 



No movement of the wall of the tentacle has been 

 observed, and the cause of the production of this 

 stream is still unknown. 



As has been already observed, the simplest mode of 

 digestion (the intracellular) is not confined to the 

 Protozoa ; it has 

 been observed in 

 Sponges, Coelen- 

 terata, and the 

 lowlier worms. 

 A clear idea of 

 what is under- 

 stood by this 

 method will be 

 obtained from 

 the consideration 

 of a single case. 

 When a section 

 is made through 

 the body walls of 

 a Hydra we 

 find that the en- 

 dodermal cells 

 vary cons i d e r - 

 ably in size, and 

 that, while some 

 are provided 



with a Single long Fig. 52.-Longitudmal Section of the Body of 

 ,, ,, a Hydra, killed m full digestion, 

 tiageilum, Others ec< Ectoderm; en, endoderm; mp, muscular pro- 

 are distinctlv cesses; d, a diatom ;/, food particles. (After 



amceboid in 



form, and give off large pseudopodia (Fig. 52) ; within 

 these cells dark-coloured granules of various sizes are to 

 be detected, and these food-particles are sometimes 

 found to be " half in and half out of the protoplasm " 

 (T. J. Parker). In such a form, therefore, as the Hydra, 

 there would not seem to be, as in Man and most of 



