226 



Elementary Biology. 



FIG. 116. LONGITUDINAL SECTION OF THE BODY 

 WALL OF Hydra. KILLED DURING DIGESTION. 

 (T. J. Parker.) 



the ectoderm. The cells are large and irregular, and are at 

 one time furnished with one or more cilia ; at other times 

 they are amoeboid and throw out blunt pseudopodia. They 

 rest on a fine structureless lamina, which again supports 

 the neuro- muscular layer above mentioned. It is a point 



of considerable biologi- 

 cal interest to find, as 

 we do in Hydra viridis, 

 chlorophyll corpus- 

 cles, more especially 

 when we learn that 

 these have the power 

 of decomposing car- 

 bonic acid just as in 

 the plant. 



Food material taken 

 into the mouth disin- 

 tegrates in the enteron, 

 and the food particles 

 are taken into the in- 

 terior of the endoderm 

 cells, which lose their 

 cilia and become am- 

 oeboid for the purpose- 

 In the interior of the 

 endoderm cells the 

 food particles gradually 

 become transformed 

 into soluble food-stuffs 



termed peptones. This process is known as intracellular 

 digestion, and is of common occurrence in many of the 

 lower animals. The other parts of the body are no doubt 

 nourished by osmosis of the soluble peptones from cell to 

 cell. The excreta and useless parts of the food are ejected 

 by the mouth. 



This account of the structure and physiology of Hydra 



ec, ectoderm ; en, endoderm ; mp, neuro-muscu 

 lar fibres ; d,f, food particles. 



