RESTITUTION-BODIES AND FREE TISSUE-CULTURE IN SYCON 319 
3. The development of these masses consists primarily in 
the sorting-out of the dermal and gastral cells. The former 
produce a single-layered epithelium, below which spicules are 
subsequently formed, the latter a central mass which later 
becomes a hollow one-layered sac, into whose cavity the cells 
put forth collar and flagella. Thus their fate is not a function 
of their position in the whole, but their position a function of 
their nature. 
4. The two types of spicules are formed in the same order 
as in normal development. 
5. Free tissue-cultures consisting only of collar-cells can be 
obtained by appropriate methods. ‘These form spheres re- 
sembling choanoflagellate colonies with the collars directed 
outwards. These live for a considerable time, but do not 
regenerate other forms of tissue or produce spicules. 
6. All grades from these to masses containing an excess of 
dermal cells may be formed. They may be classified as follows : 
(a) Collar-cell spheres. 
(b) Collar-cell blow-outs. These consist of a solid mass with 
- one or more portions blown out to form a segment 
of a collar-cell sphere. 
(b 1) With active collar-cell epithelium over the whole surface. 
(b 2) With mixed collar-cell and dermal epithelium over 
the solid portion. 
(63) With dermal epithelium over the solid portion. 
(c) Normal regenerates. 
(d) Dermal blow-outs, resembling (b1), but with dermal 
epithelium over the whole surface. 
7. In almost pure collar-cell cultures, a few normal regene- 
rates may be found. In cultures consisting almost entirely of 
collar-cell blow-outs, a few dermal blow-outs may be found. 
This is probably due to mutual attraction of dermal cells. 
8. Normal regenerates are more viable than  collar-cell 
spheres or collar-cell blow-outs of type (b iL): 
9. Dermal blow-outs may be formed from collar-cell blow-outs. 
They are in such cases produced more readily from large masses. 
10. Numerous methods have been tried for feeding the 
collar-cell spheres and blow-outs, but so far without suecess. 
