INTRODUCTION. 



If I venture to treat liere at large, witli the help of my 

 own research, the problem of the chlorophyll, of the current of 

 water, of the ingestion and the defecation in fresh-water sponges, 

 it is not, because there is but little known about these problems. 

 On the contrary ; investigators have already studied them since 

 decennaries. We even possess a great number of papers on these 

 subjects; some of which are considered in literature as standard 

 researches giving decisive results. Nevertheless, I think it neces- 

 sary to treat those problems once more; in the first place, be- 

 cause during my investigations, which I have continued as exact 

 as possible for at least 4 years, several of these results obtained 

 and generally acknowledged — some of them being of the greatest 

 interest — proved to me absolutely inexact ; and in the second 

 place, because I will be able to confirm by new and better proofs 

 some of the results, which have not yet been generally acknow- 

 ledged in consequence of a less complete argumentation. 



I will mention in short the chief points (see also van Trigt, 57b) : 

 1. In 1882 Brandt (8, 9) came to the conclusion, that the 

 chlorophyll corpuscles of the fresh-water sponges were unicel- 

 lular algae (Zoochlorellae), morphologically and physiologically 

 independent of their hosts. Ray Lankester (35) and Geddes (22), 

 however, got to quite the opposite view : the chlorophyll corpuscles 

 of Spongilla are identical to those of the plants, the investigators 

 who think them to be parasitic algae are misled. Brandt's proofs 

 are good enough, but not yet quite sufficiënt ; he did not succeed 

 in convincing Lankester and Geddes. Nevertheless, Brandt's 



