183 



18. Also some other views were given concerning the asso- 

 ciation of sponge and green alga (p. 114 — 116). 



19. Some cases were mentioned, in which quite other algae 

 (than the normal ones) occurred in a great number in the tissues 

 of Ephydatiae, viz. two filamentous algae and an unicellular one. 

 The two former proved to destroy the sponge tissue; the latter, 

 on the contrary, was finally conquered by the sponge (p. 115 — 

 118, Fig. 43—52). 



B. 



20. The current of water through the canalsystem of the fresh- 

 water sponges is caused by the flagellar motion of the choanocytes 

 in the flagellated chambers. By studying isolated choanocytes as 

 well as wholly intact flagellated chambers we could state, that 

 this motion (in normal condition) takes place in a spiral- or an 

 undulating-line, namely in a very rapid succession of waves of 

 small amplitude passing along the flagellum from the base to the 

 top (p. 124 — 132, Fig. b6a, 59); by which a current of water 

 arises straight through the axis of the flagellar spiral and simi- 

 larly in the direction from base to top, while the water flows 

 on at the side of the base (p. 126 — 128, Fig. 56rt). Exhaustion 

 causes quite different motions of the flagellum, with abnormal 

 current of water (p. 127—128, 131, Fig. 5Gh-d). The whole water- 

 current within a flagellated chamber is of course the resultant of 

 the little currents caused by each flagellum separately ; it is rapid and 

 regular (p. 132 — 133, Fig. 63). In order that a powerful and steady 

 current may be maintained by the chamber, and that, therefore, 

 the water will flow in quickly and exclusively at the prcfsopyles 

 and flow out by the apopyle, the structure of the flagellated 

 chamber must comply with definite requirements; these require- 

 ments were studied (p. 137, 133—136). 



C. 



21. By studying the phenomena of ingestion of food in nor- 

 mally living microscopic preparations of sponge tissue, I could 

 state that in fresh-water sponges: 



