INTRACELLULAR DIGESTION OP INVERTEBEATES. 95 



than to find amoeboid cells of the mesoderm, which both ingest 

 and absorb food particles. It has long been known that 

 sponges are nourished by means of amoeboid cells j but the 

 morphological value of such elements was unknown. After I 

 had suggested^ that they were to be compared to the true 

 mesoderm of other creatures, F. E. Schultze- proved, by the 

 discovery of a true ectoderm, and by a careful histological exa- 

 mination of the cells in question, the correctness of my view, 

 which has since been generally accepted. It is also gene- 

 rally believed that these mesoderm cells play an important part 

 in the nourishment of the organism ; some observers (Balfour, 

 von Lendenfeld) attributing the function of ingestion to these 

 cells alone, while others allow the endoderm some share in the 

 process. I will not stop to discuss this point, because, in the 

 first place, it is for the moment of no importance to us whether 

 the endoderm ingests or not ; and, secondly, in a future paper 

 on the endoderm, I hope to enter fully into the question. I 

 have only mentioned sponges at all in order to remind the reader 

 that ingestion by the mesoderm is an established fact among 

 them — a point which will be of use to us in discussing the 

 higher forms. 



Leaving, then, the Porifera, I must refer to the observations 

 on the ingestion of granules of colouring matter by blood-cor- 

 puscles among the lower Invertebrates. HaeckeP was the first 

 to show that when a Tethys is injected with indigo, the gran- 

 ules are taken up by the blood- corpuscles. Later on he proved 

 the occurrence of similar phenomena in the blood of various 

 Invertebrates. Haeckel, however, did not perceive the close 

 analogy between this process and the mesodermic nutrition of 

 sponges; indeed, he subsequently^ contradicted the statements 

 of Lieberkiihn as to the functions of the wandering cells of 

 Spongilla. His observations on the blood-corpuscles became 



> " Zur Entwicklungsgesch. d. Kalkschwamme," 'Zeitschr. f. wiss. Zool. ' 

 xxiv, p. 10. 



2 "Ueb. d. Bau u. d. Eutwickl. von Sycandra Raphauus," ' Zeitschr. f. 

 wiss. Zool.,' XXV, suppl., p. 258. 



8 ' Kadiolarien,' 1862, p. 104. 



^ ' Die Kalkschwamme,' 1872, Bd. i, p. 372. 



