INTRODUCTION 3 



assistance of two talented pupils, Dr. Schuberg and Dr. 

 Schewiakoff. In their works upon Ciliata (1886 and 1889), 

 which were carried on in continued collaboration with me, 

 they have brought forward in support of my conception, 

 essential contributions from within the limits of this group 

 of Protozoa. On the ground of their investigations, as well 

 as of others of my own, I was able in my description of 

 the Infusoria to give a somewhat broader and more detailed 

 exposition of my view (pp. 1317, 1392). The experience 

 gained up to this point had called forth the conviction that a 

 phenomenon of fundamental importance was before us ; a 

 conviction which I expressed at that time (1888) in the 

 following words :■ — " We are here confronted with a pheno- 

 menon of the same widespread occurrence and significance 

 as the building up of higher organisms from cells, without 

 possessing at the outset a guiding and explanatory idea, just 

 as was the case with the observers of cellular tissue before 

 the cell theory had been founded." Although convinced that 

 the structure of protoplasm was in general alveolar, I yet 

 thought it necessary at that time (p. 1392) to make a con- 

 cession to the theory of its spongy structure, inasmuch as I 

 admitted " that at times adjacent alveoli may break through 

 into one another, and thus a spongy structure would come 

 to be formed in places." This remark was particularly 

 inconsistent in the case of the endoplasm, since I at the 

 same time represented its nature as fluid, and such an 

 assumption excludes any idea of the kind. 



As a proof, to a certain extent, of the significance which 

 the theory of the honeycomb structure of protoplasm 

 might possess for the conception of protoplasm as a whole, 

 I also described in 1888 the consequences which result 

 from it for the growth of protoplasm, by tryiag to show that 

 the difficulty in conceiving of growth by intussusception 

 could be got over upon the basis of my theory. 



As is obvious from this proposition and from the view 

 quoted above from my work on Protozoa, I cherished the 

 idea, ever since the imiversal occurrence of such struc- 

 tures in protoplasm became clear to me, that in this 

 fact an essential reason was to be sought for many of the 



