RESTITUTION-BODIES AND FREE TISSUE-CULTURE IN SYCON 309 
The cultivation of the collar-cell spheres, if successful, 
would open out many points of interest. What, e.g., would 
happen if considerable cell-multiplication took place? The 
resemblance of the collar-cell spheres to colonial protozoa, 
and the fact that the collar-cells are the nutritive organs of 
the sponge, make the research still more interesting. Finally, 
the ease with which sheets of pure collar-cells can be obtained, 
and the fact that they will remain healthy, with expanded 
collars and active flagella, for one to two weeks without being 
fed, renders them very suitable as material. Detached tissues 
which assume characteristic form in this way and live for 
a considerable period in the normal medium may be termed 
free tissue-cultures. 
One or two interesting points concerning ingestion by the 
collar-cells may be mentioned here. 
(1) Addition of powdered carmine to a culture of choanocyte 
masses was followed within an hour or so by ingestion of some 
of the particles. Very many particles adhere to the flagella, 
so that the masses appear reddish. Such particles as find their 
way within the collar are ingested by a pseudopodial extension 
of the intrachoanal protoplasm. No extrachoanal ingestion 
was observed. 
(2) When Nitzchia was added, very few were ingested, and 
these only partially. They were usually caught, like the 
carmine particles, by the ends of the flagella, and lashed to 
and fro. This adhesive condition of the flagella is of interest. 
(In fresh dissociation cultures, finger-cells may often be seen 
adherent to the flagella and being waved from side to side with 
their beat.) Some were also seen adherent to the inner side 
of the collars. 
9, MECHANICAL SHOCK. Toxic AGENTS. 
Mechanical shock, such as repeated pipetting, or even transfer 
to a hanging drop, will cause marked changes in the cells, both 
dermal and choanocytic. A collar-cell blow-out treated in this 
way shows marked reduction of the size of the blow-out region, 
Ware 
