176 



of the cells. Therefore one should sharply distinguish them from 

 the food- and the defecation- and excretion vacuoles, the contents 

 of which of course belong to the cells themselves. Lieberkühn 

 (39) already drew attention to this. 



III. 



We have a very easy criterion to make out whether a fresh- 

 water sponge, in which there are neither gemmules nor finger- 

 shaped branches, is a Spongilla lacustris or an Ephydatia fluvia- 

 tilis, viz. in its smell. Spongillae, namely, have a pungent smell 

 (pungent for instance as formol); while Ephydatiae entirely lack 

 it. Several persons have, on my request, stated this difference; 

 but it also proved to me that not everybody is able to notice it. 



SUMMARY. 



This summary gives the chief results of my research, and the 

 pages of the text, the tables and illustrations concerning them. 

 See also van Trigt 57b. 



A. 



1. The two chief forms of Spongilla lacustris and Ephydatia 

 fluviatilis are a grass-green and a colourless (creamy-white) one 

 (p. 15-16, Fig. 1, 2). 



2. The sponge owes its green colour to numerous little green 

 corpuscles present in its tissues, especially in the amoebocytes 

 (p. 16 — 17, Fig. 4, 69). 



3. These green corpuscles produce O2 (p. 18 — 20, Table 1, 2) 

 and photosynthesise (oil) in light (p. 20 — 21, Table 3), but not 

 so in darkness. Consequently — • in connection with the points of 

 similitude already known (p. 17) — we are justified in declaring 

 that the green colouring-matter of the Spongillidae is identical 

 with vegetable chlorophyll (p. 21). 



