185 



canals in an apparently undifferentiated plasmic substance (p. 

 160—168, Fig. 76, 77, 73), that in reality consists of amoeboid 

 cells (p. 169—171). 



25. Defecation perhaps also can take place at the outer sur- 

 face of the sponge (p. 169), but I have never observed choanocytes 

 performing the function of excretion or defecation (p. 169). 



F. 



20. The common opinion, that the ground-substance of the 

 parenchyina, the mesogloea, should be an undifferentiated inter- 

 cellular plasmic substance, proved to me not right for Spongilli- 

 dae. The mesogloea entirely consists of amoeboid cells, just as 

 LiEBERKÜHN and Weltner stated (p. 171 — 175). 



Leyden, Zoological Laboratory, 

 August 1918 



