THREAD-CELLS OF HELIANTHOIDA. 



553 



latter by transmitted light. And thin sections of various Fossil 

 Corals of this group 



are very striking ob- Fig. 285. 



jects for the lower 

 powers of the Oxy hy- 

 drogen Microscope. 



428. The chief point 

 of interest to the 

 Microscopist, how- 

 ever, in the structure 

 of these animals, lies 

 in the extraordinary 

 abundance and high 

 development of those 

 1 Filif erous Capsules, ' 

 or 'Thread -Cells, 'the 

 presence of which on 

 the Tentacles of the 

 Hydraforin Polypes 

 has been already 

 noticed (§ 410), and 

 which are also to be 

 found, sometimes 

 sparingly, sometimes 

 veiy abundantly, in 

 the Tentacles sur- 

 rounding the mouth 

 of the Medusae, as 

 well as on other parts 

 of their bodies. If a 

 Tentacle of any of 

 the Sea-Anemones so 

 abundant on our 

 coasts (the smaller 

 and more transparent 

 kinds being selected 

 in preference) be cut- 

 off, and be subjected 

 to gentle pressure 

 between the two 

 glasses of the Aquatic- 

 Box or of the Com- 

 pressorium, multi- 

 tudes of little Dart- 

 like organs will be 



Filiferous Capsules of Helianthoid Polypes :— a, b, Corynactis Allmanni; 

 c, E, f, Caryojthyllia Smithii; d, g, Actinia crassicornis ; H, Actinia Candida. 



