INTEAOELLULAR DIGESTION OF INVEETEBEATES. 99 



atrophies, being devoured by amceboid mesoderm cells around 

 it j so that there remains in the watch-glass an apparently 

 normal Pilidium, only with its rudimentary nemertine re- 

 placed by a number of amceboid cells, full of food-granules. 



In all these cases the material eaten by mesoderm cells has 

 been formed from the body of the animal itself, and has only 

 become useless at the moment of its being devoured. These 

 cells can easily be proved capable of ingesting, and usually of 

 digesting, material altogether foreign to the organism in which 

 they live. If a large number of transparent creatures (larval 

 or adult), which possess a mesoderm, be taken fresh from the 

 sea, it is easy to find, among a number of empty mesoderm 

 cells, some containing foreign particles which may be of very 

 different kinds. In the mesoderm cells of Echiuoderm larvae 

 I have often found empty thread-cells. Similar structures 

 can often be found in Ctenophora and Pilidium. I believe 

 that bodies such as these, when found in the mesoderm cells, 

 have pierced through the body wall, and then been swallowed. 

 Just beneath the epidermis there is generally present a whole 

 multitude of amoeboid cells, ready to take up anything which 

 may pierce the body wall. In my early investigations on the 

 intra-cellular digestion of Ctenophores^ I saw that carmine 

 granules suspended in water passed, not only into the endc- 

 derm cells, but also into those of the mesoderm; though I 

 could not then determine the exact mode of their entry. 



These phenomena — on the one hand the process of resorp- 

 tion, on the other the frequent enclosure by mesoderm cells of 

 foreign bodies — show how extremely well developed is the 

 power of ingestion and absorption in these cells. I have, 

 therefore, made several experiments with the object of defining 

 more clearly the extent of this property. I chose for this 

 purpose Bipinnaria asterigera and Phyllirhoe buce- 

 phalum, because these animals are not only transparent, but 

 large enough to admit of the performance upon them of simple 



' "Ueber die intracellulare Verdauung bei Coelenteraten," ' Zool. Atiz.,' 

 1880, p. 262. 



