TYPES OF CCELENTERA HYDRA. 



'33 



of some of the cells, and it has been noticed that the same cell ma)- be 

 at one time flagellate and at another time amruliuid (cf. the cell-cycle, 

 p. 96). After this direct absorption the food is digested within the 

 cells, and while some of the dark granules seen in these cells may be 

 decomposed pigment bodies, others seem to be particles of indigestible 

 debris. Thus Hydra illustrates what is called intracellular digestion, 

 such as occurs in Sponges, some other Ccelentera, and some simple 

 " worms." But experiments show that some of the food may be 



Sim 



/»;^^ c 



En - d \» \t It !• I •' 



"1 H 



/T! 



B 



•4' 



1 I 



D 



JL = 



\i 



(f^ J 



E 



Fig. 57. — Minute structure of Hydra. — After T. J. Parker and Jickeli. 



A. Ect., ectoderm ; mg., mesoglceal plate ; st.c, stinging cell ; End., endo- 



derm with flagella and amoeboid processes. 



B. nc, nerve cell, and st.c, stinging cell. 



C. Stinging cell with ejected thread ; «., nucleus. 



D. Mesoglceal plate (mg.) with contractile roots resting on it. 



E. m.c, muscular cell with contractile roots, c.r. 



digested in the gut cavity, and subsequently absorbed. Thus it seems 

 that both intracellular and extracellular digestion occur. 



Some of the endoderm cells have muscular roots like those of the 

 ectoderm. They lie on the inner side of the middle lamina, in a trans- 

 verse or circular direction. A few cells near the mouth and base are 

 described as glandular, and the presence of a few stinging cells has 

 been recorded, though some suggest that the last are discharged ecto- 

 dermic nematocysts which have been swallowed. 



