A86 THE DEPTHS OF THE SEA. [CHAP. X. 
more so towards the distant ends, where the tubes 
contract slightly to an open orifice. At the proximal 
end, at the junction between the tube and the 
sponge body, there is also a contraction, and a slight 
pit-like involution of the surface of the sponge. 
Fic. 84.—‘ Choanites.’ Ina flint from the white chalk. 
There is something very characteristic in this pecu- 
liar form of junction which it is not easy to define, 
but which almost forces the conviction that there is 
the closest relation between these recent forms and 
tube-bearing fossil sponges such as Choanites. 
Professor Martin Duncan mentions several corals 
