92 DE. ELIAS METSOHNIKOFF. 



considerable quantity has entered the substance of the ecto- 

 derm of the uematocalyces, I have many times repeated 

 this experiment, and always with the same result. Though 

 one cannot conclude, from this one observation, that the 

 nematocalyces fulfil the function of collecting food, yet the 

 fact was striking enough to invite further investigation. Ex- 

 amination shows that these organs send out from their pro- 

 jecting extremities various kinds of pseudopodia, which attach 

 themselves either to a calyx, or to its contained polyp, or more 

 frequently flatten themselves out round the stem, so as almost 

 to encircle it. The ectoderm cells of these free extremities 

 are not distinguishable one from another, but fuse into a 

 common protoplasmic mass, which sends out some few pseu- 

 dopodia. The slow, creeping movements of the ends of the 

 nematocalyces probably serve to clean the neighbouring polyps 

 — a function which accounts for the frequent presence of foreign 

 particles in their ectoderm. Striking results are obtained by 

 studying colonies which have been for some little time in a 

 watch glass. Plumularia polyps, like so many of their allies, 

 are very delicate organisms, which only live a short time after 

 gathering. The whole colony does not, however, die, but only 

 the polyp-heads ; the coenosarc and nematocalyces survive, 

 and will, under favorable conditions, produce new polyps. The 

 last-named organs, in these circumstances, serve to eat up the 

 dying hydranths — an operation I have witnessed repeatedly in 

 both the species of Plumularia I have examined. After the polyp 

 has retracted its tentacles, and become a mere rounded mass, the 

 free end of a nematocalyx creeps into the theca, and gradually 

 absorbs, by means of its ectoderm, the whole contents of the cup. 

 So that on the second day after gathering, when most of the 

 polyps have vanished, the ectoderm of the nematocalyces is seen to 

 contain a large number of foreign particles of different kinds. 



It is further evident, on examining the loaded nematocalyces, 

 that the ingested material remains in the ectoderm, and is not, 

 as seemed to me possible, passed on to the endoderm. For a 

 few days after this, no marked alteration takes place, so that 

 I can only put it forward as a hypothesis that the ingested 



