OTHER PROTOPLASMIC MOVEMENTS 305 



to changes of surface-tension that the addition of alcohol to an emulsion of oil in 

 water favours the fusion of the oil-drops, while, partly owing to this cause and partly 

 owing to the solution of impurities, the addition of nitric acid to an emulsion of 

 partially oxidized mercury produces a sudden coalescence of the droplets. 



A high cohesion of the peripheral layers may aid in preventing fusion, as may 

 also the secretion of gelatinous membranes ; but the causes which determine fusion 

 have not as yet been satisfactorily determined in a single case. Klebs * found that 

 the gametes of Protosiphon botryoides do not conjugate at 26 to 27C., although they 

 develop and swarm at this temperature, but the causes of this behaviour, as well as 

 for the absence of any power of fusion between the swarm-cells of Aethalium when 

 first produced, are quite unknown. Townsend 8 found that fusion often does not 

 occur between the fragments of the protoplast separated by plasmolysis, possibly 

 because of the de'bris formed between them by the disorganization of connecting 

 protoplasmic threads. When the latter remain intact fusion always occurs, since the 

 most minute local union suffices to produce ultimate total fusion. The union of the 

 plasmodia of Myxomycetes is not, however, prevented by the intervention of a thick 

 layer of foreign substances, since the pseudopodia bore through it and unite. 

 Similarly, the ectoplasm affords no obstacle to complete fusion, since its high cohesion 

 is lost when it becomes withdrawn internally. Indeed the protoplast may, when 

 necessary, dissolve away intervening cell-walls, while, on the other hand, the segmenta- 

 tion into separate protoplasts may take place without any production of dividing 

 walls. 



The ingestion and excretion of solid bodies. The continued existence of symbiotic 

 algae in the cells of Hydra viridis and of certain Protozoa shows that special conditions 

 determine whether foreign bodies are retained or rejected 3 . A tendency to the 

 rejection of foreign bodies is shown even in dermatoplasts, as for instance when 

 excreta, such as calcium oxalate crystals, are thrown into the cell-sap. Usually the 

 excretion is aided by the existence of protoplasmic movement, whereas particles of 

 various substances lying against the non-motile peripheral layer of a plasmolysed 

 protoplast free from its investing cell-wall are usually not ingested. According to 

 Rhumbler 4 , differences of surface-tension and spreading tendencies are solely 

 responsible for the ingestion of foreign bodies, but this can hardly apply to all 

 cases. A solid body in contact with a drop of chloroform in water will be ingested 

 by it as the result of the chloroform spreading over it and surrounding it. In the 

 same way a glass fibre covered with shellac will be ingested by a drop of chloroform, 

 and expelled when the shellac has been dissolved away, since as soon as the tip of the 

 thread is exposed, the changed surface-tension and the tendency to spread causes 

 the chloroform to be driven away from the thread by the water 5 . 



It is, therefore, quite possible that the digestion within the protoplast of an 

 ingested body might produce the conditions for the excretion of indigestible remains. 



1 Klebs, Bedingungen d. Fortpflanzung, 1896, p. 209. 



2 Townsend, Jahrb. f. wiss. Bot., 1897, Bd. xxx, p. 495. 



3 Pfeffer, Aufnahme u. Ausgabe ungeloster Korper, 1890, p. 174. 



* Rhumbler, Archiv f. Entwickelungsmechanik, 1898, Bd. VII, p. 224. 

 5 Rhumbler, 1. c., p. 250. 



PFEFFER. Ill X 



