ILLUSTRATIONS. 



EXPLANATION OF PLATES n» I— VL 



For clearness' sake many figures have been drawn more or less dia- 

 grammatically from nature. For each object (.„symbiotic" alga, flagellated 

 chamber., etc.), however, at least one illustration true to nature has always 

 been given. 



Fig.' 1. Living green Spongillae lacustr. in water (natural size). The sponge- 

 crust cannot be seen. As for the discussion, see p. 15—16. 



Fig. 2. Living colourless Spongillae lacustr. (natural size) in water, show- 

 ing oscular tubes. The sponge-crust cannot be seen. See p. 15 — 16. 



Fig. 3. Living Spongilla growing on coverglass (magnif. 4 times). 1. = old 

 centre; ?. = newly formed membrane. See p. 12 — 13. 



Fig. 4. Isolated living amoebocyte of Spongilla grown on coverglass (magnif. 

 ± 1000 times), nu. = nucleus; gr. alg. = green chlorophyll cor- 

 puscles. See p. 17, 175. 



Fig. 5. Living green chlorophyll corpuscle of Spongillides (= „symbiotic"' 

 alga). Magnif. ± 6600 times, ch.p. = chloroplast; odr. = oildrop. 

 See p. 24—25. 



Figs. 6 — 11. Plasmolysis in the „symbiotic" algae of Spongillidae. The hea- 

 vily dotted portion represents the chloroplast; the slightly dotted 

 one the protoplasm. See p. 26. 



Figs. 12—31. Different stages of the living green „symbiotic" algae of Spon- 

 gillidae. Figs. 16—22, 25—29, 31 stages of division. The dotted 

 portion represents the chloroplast. See p. 24, 30—33. 



Figs. 32 — 34. Plural stages of division of the green „symbiotic" algae of 

 Spongillidae. The dotted portion represents the chloroplast. See p. 33. 



Figs. 35—37. Colourless stages of the „symbiotic" algae of Spongillidae. 

 Fig. 35 represents a „colourless alga with clear structure"; Fig. 36 

 a „colourless one with shade of structure" ; Fig. 37 a „colourless 

 one without structure". See p. 36, 42. 



Figs. 38—42. Green „symbiotic" algae of Spongillidae killed, and stained 

 by methylene-blue or haematoxyline. In Fig. 38 and 39 the oildrops 

 have been stained. See pag. 25 — 26. 



Figs. 43 — 45. Filamentous algae infecting Ephydatia (magnif. ± 350 times). 

 See p. 117. 



Figs. 46 — 52. Unicellular alga infecting Ephydatia (magnif. ± 800 times). 

 The dotted portion represents the chloroplast. See p. 117. 



