Preliminary remarks on immunity in animal kingdom 53 



of a protoplasmic action proper, but the branched digestive canal, 

 so intimately associated with the parenchyma, cannot be completely 

 isolated from the rest of the Planarian, and it is impossible to study 

 in vitro its digestive action apart from other tissues. To attain this 

 end we must turn to animals of larger size and those in which the 

 digestive organs can be isolated more easily. In the Coelenterata 

 intracellular digestion is general Many of them are so transparent 

 that they can be examined in vivo. It is easy to observe that the 

 particles of food are seized by amoeboid processes of the entodermic 

 cells and that they pass into the substance of these elements there to 

 be digested. For the systematic study of the digestive phenomena, 

 however, it is not sufficient merely to examine all that takes place in 

 the living animal. Experiment in vitro is also necessary. For this [57] 

 purpose the Actinians or sea-anemones offer us really excellent 

 material. As these animals are very common in all our seas and 

 are easily kept alive for long periods in aquaria, they have been used 

 for various researches, among others for the study of the process of 

 digestion. 



The Actinians are easily fed in captivity; they devour morsels 

 of flesh, of shrimps, of mollusca and other marine animals with 

 avidity. The ingenious English observers Couch and G. H. Lewes 1 

 long ago demonstrated that morsels of food when introduced enclosed 

 in perforated quills or wrapped in test paper or gutta percha silk and 

 swallowed by the anemones were afterwards ejected surrounded by 

 mucus but with no trace of digestion. Having failed in their search 

 for digestive juices in the large gastric or coelenteric cavity of the 

 Actinians, Lewes concluded that digestion in these animals is effected 

 in a purely mechanical fashion. The greatly developed muscles of the 

 Actinians were supposed to squeeze the food and extract its fluid which 

 is then absorbed by the walls of the general cavity. It was not until 

 very much later that the problem of digestion in the Actinians could 

 be resolved in any accurate and definitive fashion. More than twenty 

 years ago I demonstrated 2 that the digestion in these polyps is intra- 

 cellular. In order that a clear conception of this phenomenon may be 

 obtained it may be useful to recall in a few words the fundamental 

 features of the organisation of Actinians. They are cylindrical bodies, 

 sometimes as large as the fist, attached by their base to stones, 

 shells, or other submarine objects, and furnished at their free 

 extremity with one or more series of tentacles. In the middle 



1 G. H. Lewes, "Sea-side Studies," Edin. and London, 1858, p. 216. 



2 Zool. Anz. y Leipzig, 1880, Jahrg. in, S. 261, and 1882, Jahrg. v, S. 310. 



