J 2 



of a culture of chlorophyll corpuscles ; but I did not succeed. Next 

 I tried to pick up a single chlorophyll corpuscle from a drop of 

 water by means of Schouten's apparatus, in order to transport 

 it to the sterile gelatine. The apparatus, which proved good for 

 bacteria, was of no use to me: in water the corpuscle sticks to 

 the needle, but it immediately loosens when taken out; and my 

 efforts to get a more appropriate form of needle-point were un- 

 successful. 



So I did not get a pure culture of the chlorophyll corpuscles of 

 the Spongillidae. But this was of no consequence to my research ; 

 the ordinary cultures procured all results I wanted. 



Microscopic preparations. As I stated already in the Intro- 

 duction, I did not use any other than living preparations; namely 

 in two forms : 



1. Ravel preparations of a sponge tissue, or preparations of 

 chlorophyll corpuscles from a culture, made on a glass-slide with 

 a drop of the original liquid; the coverglass surrounded by 

 vaseline in order to entirely separate the preparation from the 

 outer world. 



2. Sponges grown on coverglass. These preparations, in which 

 I observed many important phenomena in sponge life, were made 

 in the following way : A branch of a Spongilla — Ephydatia is not 

 appropriate for the experiment because of its slow growth — is 

 cut at full length in two^ and each half is divided again into short 

 pieces of 1 c.M. Each piece is then put on its long flat side on 

 a large coverglass into an aquarium. When kept quiet, these little 

 sponges will then soon attach themselves with this side (the wound 

 side) to their glass; while a thin membrane of newly formed 

 sponge-tissue will even extend from each old sponge piece as a 

 centre over the coverglass (Fig. 3). Tliis membrane thickens ac- 

 cording as it is growing older. In a week's time we then possess 

 in this membrane a wholly intact, normally living 

 sponge preparation, fit for microscopic examination even 

 with an oil-immersion! To that purpose we put the cover- 

 glass, the sponge at the underside, on glass feet into a glass vessel 

 filled with water, so, that the upperside of the coverglass remains 



