486 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 tuhe and the 

 sponge body, there is also a contraction, and a slight 

 pit-like involution of the surface of the sponge. 

 There is something very characteristic in this pecu- 



Fio. 84.' Choanites.' In a flint from the white chalk. 



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 



