106 DR. BLIAS METSCHNIKOFF. 



are eaten by mesoderm cells, just as are the similar granules, 

 found during metamorphosis; so that the amoeboid cells of 

 the arms are often crammed with debris. In addition to 

 the clear, feebly refracting degradation products, one often 

 finds in the ectoderm of Bipinnaria masses of small, 

 round, strongly refracting bodies which are devoured by 

 the mesoderm cells. I have not been able to determine 

 exactly the nature of these bodies, but it seems possible that 

 they may be spores of bacteria, since they closely resemble 

 undoubted spores, while it can be shown that the mesoderm 

 cells will readily ingest such bodies. If fluids containing 

 bacteria be injected beneath the skin of Bipinnaria or Phyl- 

 lirhoe, or if they develop spontaneously in the wounds of such 

 animals, they will soon be found within the substance of many 

 amoeboid mesoderm cells. Both still and motile forms are 

 thus ingested, and they may be found either embedded 

 in the protoplasm of the absorbent cell, or surrounded by 

 a vacuole. Individual bacteria are often seen which retain 

 their power of movement even after ingestion, while in 

 other cases the motility is lost at once, and the whole 

 bacterium becomes so delicate as to be scarcely visible. 

 We may then consider that bacteria are habitually ingested 

 by mesoderm cells, when they make their appearance in the 

 organism ; — a fact which obviously increases the prophylactic 

 importance of these cells. These phenomena can perhaps be most 

 easily seen in Botryllus, colonies of which, when freshly gathered, 

 contain almost invariably large quantities of bacteria within 

 the test ; I found especially a Spirochoeta, closely resembling 

 the S. Obermeyeriof relapsing fever, and a small Bacillus, 

 like the Lepra bacillus, which had a spore at each 

 end. Both these forms were pursued by the wandering cells 

 of the Botryllus, and were found ingested and absorbed by 

 them in various stages of development. The victory was not, 

 however, all on one side ; here and there were found mesoderm 

 cells to all appearance dead, with long bacterial filaments pro- 

 jecting from them. 



The same thing has been observed in Vertebrates, where 



