CCELENTERATA. 



21 



contains a large nucleus with nucleolus. Adjacent cells touch 

 one another externally, whilst, internally, spaces are left between 

 them which are occupied by interstitial cells (ic). .These are small 

 nucleated cells present in all parts of the body but the foot, and 

 often crowded together so as to obscure their individual outlines. 



/ 



ec. 



Fig. 4. HYDRA, various scales. A, Budding specimen of H. fusca 

 extended; A', ditto, retracted; B, tranverse section of H. fusca; 

 B', part of same on larger scale; C, isolated tailed cells; D, isolated 

 thread -cell, from H. viridis; f, foot; ra, mouth; tn, tentacles; 

 ec, ectoderm; en, endoderm; 6, bud; or, typical position, &c., of 

 ovary; t, do., of testes; i.l, intermediate lamella, the dots above this 

 represent the cut ends of "tails;" i.c, interstitial cells; n, thread-cells; 

 /, flagella; fd, organism (in B) in digestive cavity, as food. 



