INTRODUCTION II 



alization was made without adequate observation, for at first he 

 denied the presence of a mouth as well as anus. 



Dujardin further showed that the motile organs of the Protozoa, 

 whether cilia, flagella, or pseudopodia, are mainly the prolongations 

 of the outer coatings of the organism, and are in no sense similar to 

 the hairs of higher animals, and he even suggested the transition, 

 which has since been shown to occur, between the simplest of pseu- 

 dopodia and the more complex flagella. He contradicted Ehrenberg's 

 theory as to the function of the contractile vacuole, reverting to the 

 interpretation given by Spallanzani. He also denied the complexity 

 of the reproductive organs, as described by Ehrenberg, but made a 

 singular mistake in regarding the granules inside of the body as 

 germs. 



Many besides Dujardin had begun to criticise Ehrenberg's theory. 

 Carus ('32) insisted, on purely theoretical grounds, that animals must 

 exist whose structure is as simple as that of an egg, since all animals 

 begin with the simple egg structure. Two years later, he criticised 

 Ehrenberg's theory, on the ground that inner circulation of the plasm 

 in Paramcecium (discovered by Gruithuisen, '12), which resembles 

 the circulation in the plant Chara, does not accord with Ehrenberg's 

 description of the digestive apparatus. A similar objection was 

 raised by Focke ('36), based on observations upon the streaming 

 plasm in Vaginicola and Paramcecium. 



The first suggestion that Protozoa might be single cells was made 

 by Meyen ('39), who compared the entire infusorian body to a single 

 plant-cell. The cell-theory, according to Butschli, however, was first 

 applied directly to the Protozoa by Barry ('43), who asserted that 

 Monas and its allies among the Flagellidia are single cells, and that 

 the nucleus found within them is the equivalent of the cell-nucleus 

 of higher animal forms. At the same time Barry expressed the view 

 that cells increase only by division, and he compared the processes of 

 multiplication in Volvox and Chlamydomonas with the cleavage of 

 eggs which he, with Schwann, regarded as single cells. 1 



Barry's view was accepted in part by Owen, who thought, however, 

 that the Infusoria could not be included with the Flagellidia as single 

 cells, because of their higher differentiation. It was von Siebold 

 {'48), however, who finally asserted the unicellular nature of all 

 Protozoa. 



Ehrenberg's theory was not given up without a struggle, and, 

 among others, we find Schmidt ('49) coming to his support with the 

 fact that the trichocysts, or stinging threads of the Infusoria, found by 

 Ellis ( 1 769), and by Spallanzani ( 1 776), and the contractile vacuoles 



iCf. Butschli ('83), p. 1 153. 



