Preliminary remarks on immunity i^i animal kingdom 51 



rounded and fused together, but the nucleus and the haemo- 

 globin enable us to recognise them without any difficulty. Later 



Fig. 7. Intestinal cell of a 

 Planarian, filled with red 

 blood corpuscles, undergoing 

 digestion, of the goose. 



Fig. 8. Digestion of red blood 

 corpuscles of the goose with- 

 in an intestinal cell of a 

 Planarian. 



the red colouring matter begins to diffuse into the digestive vacuoles 

 which form around the corpuscles. These corpuscles empty them- 

 selves, retaining their nuclei and capsules, which shrivel more and 

 more. The nucleus also undergoes almost complete digestion, its 

 membranous layer alone persisting (fig. 8). Even several days after 

 the digestion of the blood has begun one can still find debris of 

 perfectly recognisable red corpuscles, but the red colour has been 

 replaced by a more or less pronounced brown tint. In the last 

 stage of the digestive process, as the red corpuscles disappear, the 



4—2 



