306 THE PROTOZOA 



based upon a comparison with our own consciousness or upon physical 

 phenomena in the non-living world, must be considered only tenta- 

 tive. If protoplasm be regarded merely as a fluid substance, or 

 better, a mixture of various, different fluids, forming an exceedingly 

 complex chemical substance distinct in its individuality, and possess- 

 ing certain recognizable properties, then it must be subject to the 

 same laws which govern all fluids, and many of the so-called vital 

 phenomena can be reduced to processes which in the inorganic world 

 are familiar to physicists and chemists. Haeckel ('66) pointed out in 

 connection with the supposed selective power of Protozoa, that an 

 alum crystal selects only alum molecules from a mother liquid holding 

 numerous salts in solution, and Berthold ('86) suggested that lifeless 

 fluids will not absorb all kinds of stuff, but only such as have a certain 

 chemical composition. Verworn ('89), experimenting with Amceba 

 and Pelomyxa, found no selective action with the objects used ; every- 

 thing was surrounded by the pseudopodia and drawn into the body. 

 On the other hand, certain Rhizopoda (as in the case of Vampyrella 

 spii'ogyrce, which feeds solely on Spirogyra) eat only certain kinds of 

 food, while Heliozoa, according to Meissner ('88), and Reticulariida, 

 according to Verworn ('89), normally take in only living organisms as 

 food. The latter, suspecting that in such cases it is only 

 the mechanical irritation of moving organisms which causes the 

 pseudopodial reaction, experimented with inorganic objects, such as 

 a needle-point, a bit of paper, etc., and found that Actinospharium 

 among Heliozoa, and Polystomella among marine rhizopods, will 

 absorb a moving needle-point or a bit of paper as readily as a strug- 

 gling ciliate, and he concluded that the direct cause of food absorption, 

 in these cases at least, was the mechanical stimulus. Again, in forms 

 which draw food to the mouth opening by means of a vortex current 

 due to flagella or cilia, Entz ('88) assumed a selective action from the 

 fact that certain objects are passively thrown out of the current and 

 do not reach the mouth opening at all. Stein accounted for the same 

 occurrence by attributing a function of taste to certain of the adoral 

 cilia. But Verworn called attention to the old experiments of Gieichen 

 and Ehrenberg in feeding ciliates with powdered carmine and indigo, 

 which was quickly ingested, while he also observed that digestible as 

 well as indigestible particles are thrown out of the vortex current. 

 Selection in such cases is not subjective, but depends upon the physi- 

 cal or chemical nature of the substances; the animal itself does not 

 distinguish between good and bad. 



Even more interesting in this respect are the observations and ex- 

 periments of Rhumbler ('98) with organic and inorganic fluids. While 

 corroborating the observations of Hofer and others, that objects are 

 ingulfed at the posterior end of Amceba, he found that the ectoplasm 



