58 Chapter III 



Mesnil has fed the same Actinians with repeated doses of blood 

 with a view to make out whether the cells, tinder these conditions, 

 acquire any special aptitude for the production of the actino-diastase, 

 Notwithstanding numerous attempts, he could never assure himself 

 that this takes place ; the rapidity with which the red corpuscles were 

 dissolved by the extract of the mesenterial filaments was the same 

 whether this was prepared from Actinians that had been several times 

 fed on blood or from those that had received none at all. 



From what I have just described no doubt can exist that intra- 

 cellular digestion is not a " protoplasmic" process essentially different 

 from that which is brought about by the digestive juices secreted in 

 the intestinal canal. In both cases we have a diastatic action, due 

 to soluble ferments, produced by living elements. In intracellular 

 digestion, however, the diastases carry on digestion in the interior 

 of the cells, principally in the vacuoles, whilst in extracellular 

 digestion this process goes on outside the cells, in the lumen of 

 the gastro-intestinal canal. 



It cannot be doubted that, in the animal scale, intracellular 

 digestion represents an earlier and primitive condition for the 

 solution of the food substances. This follows from the fact that 

 it is widely distributed amongst the lowest animals, such as the 

 Protozoa, Sponges, Coelenterata and Turbellaria. Intracellular 

 digestion only gives way step by step to digestion by secreted 

 juices. The higher Invertebrata furnish us with conclusive testi- 

 mony on this point. Thus, among the gasteropod Mollusca, there are 

 some which exhibit the two modes of digestion in the same animal. 

 In Phyllirhoe, a beautiful mollusk, without a shell and quite trans- 

 parent, which floats on the surface of the sea, the food can be seen 

 passing into the cavity of the digestive canal, where it undergoes 

 a preliminary digestion by secreted juices ; the result is a magma of 

 small solid particles which are at once seized by the amoeboid 

 epithelium of the coecal appendages, two on each side of the body. 

 Intracellular digestion then completes the process and ends by 

 dissolving the nutritive substances and reducing them to their 

 final stage previous to absorption. On adding 'to the food some 

 particles of carmine these may be found along with the digestible 

 particles in the interior of the epithelial cells of the coeca. 

 [63] This example furnishes us with a real link between primitive 

 intracellular digestion and the perfected and derivative extracellular 

 digestion. In the same group of Gasteropods may be followed out 



