VACUOLESTHE TONOPLAST THEORY 231 



in plasmolysis and similar processes, in which it is evident 

 that the division of the vacuole is effected by the surrounding 

 protoplasm. Also what Went communicates later (1888) in this 

 respect is not convincing. For the proof that vacuoles become 

 constricted in two is not sufficient ; it ought rather to be proved 

 that this is effected by the proper and independent wall of the 

 vacuole, and not by means of the surrounding protoplasm. It is 

 just this point, however, which Went is not able to make clear. 

 He even says himself on p. 318, "the wall of the vacuole is so 

 thin that for the most part it is not visible," nevertheless he 

 thinks it may be assumed " from analogy " that it takes an 

 active part in the division. On p. 319 it is remarked: "It 

 hence seems to me (!) that the wall of the vacuole plays an 

 active part. This point must, however, be made clear by 

 later investigations." This point is, however, just the most 

 salient one in the whole question concerning the so-called 

 division of the vacuoles, and has, therefore, in spite of his 

 assertion to the contrary, not been solved by Went. Just as 

 little, moreover, has Went proved that the vacuoles never appear 

 as new formations, as he asserts. His investigations, as well as 

 those of de Vries, only extend, as is shown by the figures, to 

 relatively large coarse vacuoles. Now since new vacuoles are 

 originally at any rate exceedingly minute, their statements prove 

 nothing in this respect. What can, however, be proved, in such 

 subtle questions, by figures so coarsely schematic on the whole 

 as are those which accompany the works of de Vries and Went ? 

 Whoever has studied at all closely the contractile vacuoles of 

 Protozoa cannot doubt for a moment that new vacuoles con- 

 tinually make their appearance, which do not owe their first 

 origin to the division of formerly existing ones. This had 

 already been for a long time proved to a certainty when de Vries 

 and Went undertook their investigations. 1 Moreover, Pfeffer has 



1 In recent times Kiinstler (1889) has come forward energetically in defence 

 of a " more resistant membrane " being present round the contractile vacuole 

 of Flagellata, especially in the genus Cryptomonas. Both on theoretical 

 grounds, and from the special relations of the contractile vacuole of that genus, 

 he regards this conclusion as unquestionable. Without entering here into 

 details, I can only refer to the much clearer relations existing in Infusoria 

 (see on this point my book on Protozoa), in which the origin of the contrac- 

 tile vacuoles by fusion of numerous small ones has so often been proved, 

 that the presence of a special and constant membrane seems quite impossible. 

 Since a corresponding origin of the contractile vacuole has also frequently 

 been observed in Flagellata, it is impossible that the relations should be other- 

 wise here, unless the structure termed contractile vacuole in Cryptomonas 

 corresponds in some way to the reservoir of Euglenae, which I regard as quite 

 improbable. 



