410 



Mr. E. Billings on the Structure of 

 Fig. 1. Fig. 2. 



al 



^^ 



Fig. 1. The upper part of Caryocrhms ornatus, the test being removed in 

 order to show the internal structure of the fourteen hydrospires that 

 surround the summit. The parallel lines represent the flat tubes. The 

 other figures exhibit the modifications which the hydrospires undergo 

 in passing through : — fig. 2. Coclaster ; fig. 3. Pentremites witli broad 

 ambulacra ; fig. 4. Pentremites with single tubes ; fig. 5. Palfeozoic 

 Crinoids with a convoluted plate attached to the centre of radiation ; 

 fig. 6. Sand-canal or madreporic tube of a stai-fish, enclosing a doubly 

 convoluted plate ; fig. 7. Ambulacral canals of a starfish with the 

 doubly convoluted plate of the sand-canal attached to the oesophageal 

 ring. The following letters have the same reference in all the figures 



