56 Chapter III 



animals, Mesnil directed his attention to the digestion of the red 

 corpuscles of the blood. He made use of the red corpuscles of 

 [60] several species of Yertebrata, but he made a special study of the 

 digestion of nucleated red blood corpuscles. These corpuscles are 

 very delicate, and may even undergo a certain degree of maceration 

 in ordinary sea water. In spite of this these red corpuscles are not 

 digested in the coelenteric cavity of the Actinians but, once ingested 

 by the entodermic cells of the mesenterial filaments, they are com- 

 pletely dissolved by the intracellular digestion. Mesnil also observed 

 that fibrin is not digested except in the cells of the filaments. The 

 facts cited by Chapeaux in favour of an extracellular digestion in the 

 fluid of the coelenteric cavity in no way support his hypothesis, and 

 reduce themselves, according to Mesnil, to a digestion by the diastase 

 of blood itself fixed by the fibrin, after the bleeding, at the moment 

 of the formation of the clot. 



For a certain period the red corpuscles may be met with inside the 

 cells of the mesenterial filaments. They are ingested in their normal 

 state — oval red corpuscles with a nucleus. As several hours are 

 required for the ingestion, it is evident that the fluid of the coelenteric 

 cavity has been incapable of attacking the red corpuscles. In the 

 protoplasm of the entodermic cells the red corj)uscles become rounded, 

 their walls become permeable, and the haemoglobin begins to diff'use 

 from them. It passes first into the vacuoles of the digestive cells and 

 is then, in part, ejected into the general body cavity. The haemo- 

 globin is transformed into a green substance which reminds one of 

 biliary pigment. The membranes and nuclei of the red corpuscles 

 are also digested and ultimately disappear completely. 



The digestive cells of the entoderm ingest not only blood cor- 

 puscles or fibrin, but also fragments of muscular fibre and particles of 

 carmine and litmus. These latter, as already stated, indicate a marked 

 acid reaction. 



In the Actinians, then, the mesenterial filaments, or rather their 

 entodermic portion, represent the real organ of intracellular digestion. 

 There are indeed other regions of the entoderm which also carry on 

 this function, but in an insignificant degree as compared with the 

 mesenterial filaments which are capable, however, not only of 

 ingesting and digesting solid substances, but also of absorbing 

 solutions. Mesnil has demonstrated this by injecting soluble 

 [61] colouring matters, such as eosin, carminate of ammonia, etc., into 

 xictinians. These solutions, although in great part absorbed by the 



