410 



Mr. E. Billings on the Structure of 



Fig. 2. 



Fig. 1. The upper part of Caryocrinus omatus, the test beinj? removed in 

 order to show the internal structure of the fourteen hydrospires that 

 surround the summit. The parallel lines represent the fiat tuoes. The 

 other fifrures exhibit the modifications which the hydrospires undergo 

 in pa.'sinpr throufrh : — fig. 2. Codaster; fig. 3. PeHtremites with broad 

 ambulacra ; fig. 4. Pentremit^s with single tubes ; fig. 5. Pah-cozoic 

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

 fig. 0. Sand-canal or madreporic tube of a starfish, 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 



